Human infants are aroused and concerned by moral transgressions.

Humans reason and care about ethical issues, such as avoiding unnecessary harm. But what enables us to develop a moral capacity? This question dates back at least to ancient Greece and typically results in the traditional opposition between sentimentalism (the view that morality is mainly driven by socioaffective processes) and rationalism [the view that morality is mainly driven by (socio)cognitive processes or reason]. Here, we used multiple methods (eye-tracking and observations of expressive behaviors) to assess the role of both cognitive and socioaffective processes in infants' developing morality. We capitalized on the distinction between moral (e.g., harmful) and conventional (e.g., harmless) transgressions to investigate whether 18-mo-old infants understand actions as distinctively moral as opposed to merely disobedient or unexpected. All infants watched the same social scene, but based on prior verbal interactions, an actor's tearing apart of a picture (an act not intrinsically harmful) with a tool constituted either a conventional (wrong tool), a moral (producing harm), or no violation (correct tool). Infants' anticipatory looks differentiated between conventional and no violation conditions, suggesting that they processed the verbal interactions and built corresponding expectations. Importantly, infants showed a larger increase in pupil size (physiological arousal), and more expressions indicating empathic concern, in response to a moral than to a conventional violation. Thus, infants differentiated between harmful and harmless transgressions based solely on prior verbal interactions. Together, these convergent findings suggest that human infants' moral development is fostered by both sociocognitive (inferring harm) and socioaffective processes (empathic concern for others' welfare).

Great apes and human children rationally monitor their decisions.

Several species can detect when they are uncertain about what decision to make-revealed by opting out of the choice, or by seeking more information before deciding. However, we do not know whether any nonhuman animals recognize when they need more information to make a decision because new evidence contradicts an already-formed belief. Here, we explore this ability in great apes and human children. First, we show that after great apes saw new evidence contradicting their belief about which of two rewards was greater, they stopped to recheck the evidence for their belief before deciding. This indicates the ability to keep track of the reasons for their decisions, or 'rational monitoring' of the decision-making process. Children did the same at 5 years of age, but not at 3 years. In a second study, participants formed a belief about a reward's location, but then a social partner contradicted them, by picking the opposite location. This time even 3-year-old children rechecked the evidence, while apes ignored the disagreement. While apes were sensitive only to the conflict in physical evidence, the youngest children were more sensitive to peer disagreement than conflicting physical evidence.

Preschoolers agree to and enforce prosocial, but not selfish, sharing norms.

Young children act prosocially in many contexts but are somewhat selfish when it comes to sharing their resources in individual decision-making situations (e.g., the dictator game). But when deciding collectively, would they make it a binding rule for themselves and others to act selfishly in a resource sharing context? Here we used a novel "group dictator game" in a norm creation paradigm to investigate whether 3- and 5-year-olds (N = 48) would agree to and enforce a selfish or prosocial sharing norm. Children from a Western cultural background were paired with two puppets at a time. Each group member had an endowment of four stickers and faced a photograph of a recipient. In the prosocial norm condition a proposer puppet suggested to share half of one's endowment, whereas in the selfish norm condition another proposer suggested to share nothing. The protagonist puppet then either followed or violated the suggested norm. We found that 5-year-olds (but not 3-year-olds) rejected selfish proposals more often than prosocial proposals. Importantly, older (but not younger) preschoolers also enforced the prosocial (but not the selfish) norm by protesting normatively and intervening when the protagonist acted selfishly (and thus violated the norm). These results indicate that a collective decision-making context may enhance preschoolers' prosociality and that moral considerations on the content of a proposed sharing rule influence preschoolers' creation and enforcement of such nonarbitrary norms.

Older (but not younger) preschoolers reject incorrect knowledge claims.

As epistemic and normative learners, children are dependent on their developing skills for evaluating others' claims. This competence seems particularly important in the current digital age in which children need to discern valid from invalid assertions about the world in both real-life and virtual interactions to ultimately gather and accumulate robust knowledge. We investigated whether younger and older preschoolers (N = 48) understand that a speaker's knowledge claim ('I know where X is') may be correct or incorrect given objectively accessible information (about whether the speaker had perceptual access to a critical event). We found that both younger and older preschoolers accepted correct knowledge claims that matched observable reality, but that only older preschoolers reliably rejected incorrect knowledge claims that did not match reality (the speaker lacked perceptual access). Nevertheless, a considerable proportion of younger preschoolers both rejected incorrect knowledge claims and gave valid explanations, suggesting that the ability to scrutinize epistemic claims develops gradually from around 3 to 4 years of age. These findings may help integrate research on children's norm and theory of mind development. Statement of contribution What is already known on this subject? Preschoolers understand that non-epistemic claims (e.g., 'This is an X!') may be correct or incorrect, and they track a speaker's relevant characteristics in testimonial situations. It is not known what preschoolers understand about the validity of epistemic (knowledge) claims (e.g., 'I know that X'). What does this study add? Younger and older preschoolers accepted correct knowledge claims (children observed that a speaker saw a critical event and was thus knowledgeable). Only older preschoolers reliably rejected incorrect knowledge claims (the speaker did not see the critical event). Nevertheless, a considerable proportion of younger preschoolers showed competence in their evaluation of, and reasoning about, incorrect knowledge claims. Findings suggest that the ability to evaluate epistemic claims develops gradually from around 3 to 4 years of age.

Eighteen-Month-Old Infants Correct Non-Conforming Actions by Others.

At around their third birthday, children begin to enforce social norms on others impersonally, often using generic normative language, but little is known about the developmental building blocks of this abstract norm understanding. Here, we investigate whether even toddlers show signs of enforcing on others interpersonally how "we" do things. In an initial dyad, 18-month-old infants learnt a simple game-like action from an adult. In two experiments, the adult either engaged infants in a normative interactive activity (stressing that this is the way "we" do it) or, as a non-normative control, marked the same action as idiosyncratic, based on individual preference. In a test dyad, infants had the opportunity to spontaneously intervene when a puppet partner performed an alternative action. Infants intervened, corrected, and directed the puppet more in the normative than in the non-normative conditions. These findings suggest that, during the second year of life, infants develop second-personal normative expectations about their partner's behavior ("You should do X!") in social interactions, thus making an important step toward understanding the normative structure of human cultural activities. These simple normative expectations will later be scaled up to group-minded and abstract social norms.

Preschoolers Understand the Moral Dimension of Factual Claims.

Research on children's developing moral cognition has mostly focused on their evaluation of, and reasoning about, others' intrinsically harmful (non-)verbal actions (e.g., hitting, lying). But assertions may have morally relevant (intended or unintended) consequences, too. For instance, if someone wrongly claims that "This water is clean!," such an incorrect representation of reality may have harmful consequences to others. In two experiments, we investigated preschoolers' evaluation of others' morally relevant factual claims. In Experiment 1, children witnessed a puppet making incorrect assertions that would lead to harm or to no harm. In Experiment 2, incorrect assertions would always lead to harm, but the puppet either intended the harm to occur or not. Children evaluated the puppet's factual claim more negatively when they anticipated harmful versus harmless consequences (Experiment 1) and when the puppet's intention was bad versus good over and above harmful consequences (Experiment 2). These findings suggest that preschoolers' normative understanding is not limited to evaluating others' intrinsically harmful transgressions but also entails an appreciation of the morally relevant consequences of, and intentions underlying, others' factual claims.

Children's evaluation of verified and unverified claims.

Critical to children's learning is the ability to judiciously select what information to accept-to use as the basis for learning and inference-and what information to reject. This becomes especially difficult in a world increasingly inundated with information, where children must carefully reason about the process by which claims are made in order to acquire accurate knowledge. In two experiments, we investigated whether 3- to 7-year-old children (N = 120) understand that factual claims based on verified evidence are more acceptable than claims that have not been sufficiently verified. We found that even at preschool age, children evaluated verified claims as more acceptable than insufficiently verified claims, and that the extent to which they did so was related to their explicit understanding, as evident in their explanations of why those claims were more or less acceptable. These experiments lay the groundwork for an important line of research studying the roots and development of this foundational critical thinking skill.

Preschoolers, but not adults, treat instrumental norms as categorical imperatives.

Hypothetical norms apply only when agents have specific goals, whereas categorical norms apply regardless of what agents want. Deciding whether a rule is hypothetical or categorical is crucial for navigating many social situations encountered by children and adults. The current research investigated whether preschoolers viewed instrumental norms (about how to accomplish practical tasks), prudential norms (pertaining to agent welfare), and moral norms (pertaining to others' welfare) as hypothetical or categorical. A second main question was whether preschoolers draw distinctions between instrumental and other norms. Participants were interviewed about norm violations in which the agent did or did not have the relevant goal. The goal manipulation had no effect on children's judgments of permissibility; most children treated all three norm types as categorical. Nevertheless, children distinguished instrumental events from prudential and moral events along several dimensions. In contrast, participants in two adult samples treated instrumental norms, and some prudential norms, as hypothetical, but treated moral norms as categorical (applicable regardless of agent goal). These findings suggest that preschoolers do not yet reliably distinguish between hypothetical and categorical norms, yet do view rules of instrumental rationality as a distinct type of norms.

The early development of the normative mind.

Normativity is pervasive in everyday human social interactions and perhaps even constitutive of human forms of group and societal living. During the past decade, there has been increased interest in the ontogeny of normativity and the role that norms play in early social reasoning and behavior. Given the ubiquity of normativity, it is vital to investigate the development of children's normative understanding and behavior in a variety of different contexts, ranging from prosocial behavior to rational action or from linguistic competencies to cultural norms and values. Hence, in this special issue on the early development of the normative mind, researchers from different theoretical traditions have employed a number of different methods (e.g., third-party norm enforcement, judgment and reasoning, social behavior) to address different, yet related, research questions about the ontogeny of normativity. Here, we introduce the reader to the current debate and point to important research questions for the field.

Children's developing metaethical judgments.

Human adults incline toward moral objectivism but may approach things more relativistically if different cultures are involved. In this study, 4-, 6-, and 9-year-old children (N=136) witnessed two parties who disagreed about moral matters: a normative judge (e.g., judging that it is wrong to do X) and an antinormative judge (e.g., judging that it is okay to do X). We assessed children's metaethical judgment, that is, whether they judged that only one party (objectivism) or both parties (relativism) could be right. We found that 9-year-olds, but not younger children, were more likely to judge that both parties could be right when a normative ingroup judge disagreed with an antinormative extraterrestrial judge (with different preferences and background) than when the antinormative judge was another ingroup individual. This effect was not found in a comparison case where parties disagreed about the possibility of different physical laws. These findings suggest that although young children often exhibit moral objectivism, by early school age they begin to temper their objectivism with culturally relative metaethical judgments.

Young Children See a Single Action and Infer a Social Norm.

Human social life depends heavily on social norms that prescribe and proscribe specific actions. Typically, young children learn social norms from adult instruction. In the work reported here, we showed that this is not the whole story: Three-year-old children are promiscuous normativists. In other words, they spontaneously inferred the presence of social norms even when an adult had done nothing to indicate such a norm in either language or behavior. And children of this age even went so far as to enforce these self-inferred norms when third parties "broke" them. These results suggest that children do not just passively acquire social norms from adult behavior and instruction; rather, they have a natural and proactive tendency to go from "is" to "ought." That is, children go from observed actions to prescribed actions and do not perceive them simply as guidelines for their own behavior but rather as objective normative rules applying to everyone equally.

Young children's behavioral and emotional responses to different social norm violations.

From an early age, children can talk meaningfully about differences between moral and conventional norms. But does their understanding of these differences manifest itself in their actual behavioral and emotional reactions to norm violations? And do children discriminate between norm violations that affect either themselves or a third party? Two studies (N=224) were conducted in which children observed conventional game rule violations and moral transgressions that either disadvantaged themselves directly or disadvantaged an absent third party. Results revealed that 3- and 5-year-olds evaluated both conventional and moral transgressions as normative breaches and protested against them. However, 5-year-olds also clearly discriminated these types of transgressions along further dimensions in that (a) they tattled largely on the moral violation and less on the conventional violation and (b) they showed stronger emotional reactions to moral violations compared to conventional violations. The 3-year-olds' responses to moral and conventional transgressions, however, were less discriminatory, and these younger children responded rather similarly to both kinds of violations. Importantly, most children intervened both as victims of the transgression and as unaffected third parties alike, providing strong evidence for their agent-neutral understanding of social norms.

Young Children Understand the Role of Agreement in Establishing Arbitrary Norms-But Unanimity Is Key.

Human cultural groups value conformity to arbitrary norms (e.g., rituals, games) that are the result of collective "agreement." Ninety-six 3-year-olds had the opportunity to agree upon arbitrary norms with puppets. Results revealed that children normatively enforced these novel norms only on a deviator who had actually entered into the agreement (not on dissenting or ignorant individuals). Interestingly, any dissent during the norm-setting process (even if a majority of 90% preferred one course of action) prevented children from seeing a norm as established for anyone at all. These findings suggest that even young children understand something of the role of agreement in establishing mutually binding social norms, but that their notion of norm formation may be confined to conditions of unanimity.

Preschoolers understand the normativity of cooperatively structured competition.

Human institutional practices often involve competition within a cooperative structure of mutually accepted rules. In a competitive game, for instance, we not only expect adherence to the rules of the game but also expect an opponent who tries to win and, thus, follows a rational game-playing strategy. We had 3- and 5-year-olds (N=48) play for a prize against an opponent (a puppet) who played either rationally (trying to win) or irrationally (helping the children to win) while either following or breaking the rules of the game. Both age groups performed costly protest against an opponent who followed the rules but played irrationally by helping the children to win. When facing a rule-breaking opponent, 3-year-olds protested only the rule breaches of an irrational opponent but not irrational play. Five-year-olds also protested the rule breaches of a rational opponent, but in contrast to the 3-year-olds, they protested irrational behavior even in the context of rule breaches. Moreover, many children, in particular 3-year-olds, refrained from protesting. These findings suggest that 5-year-olds, but not 3-year-olds, fully understand the dual-level normative structure of cooperatively regulated competition.

Young children use pedagogical cues to modulate the strength of normative inferences.

Young children understand pedagogical demonstrations as conveying generic, kind-relevant information. But, in some contexts, they also see almost any confident, intentional action on a novel artefact as normative and thus generic, regardless of whether this action was pedagogically demonstrated for them. Thus, although pedagogy may not be necessary for inferences to the generic, it may nevertheless be sufficient to produce inductive inferences on which the child relies more strongly. This study addresses this tension by bridging the literature on normative reasoning with that on social learning and inductive inference. Three-year-old children learned about a novel artefact from either a pedagogical or non-pedagogical demonstration, and then, a series of new actors acted on that artefact in novel ways. Although children protested normatively in both conditions (e.g., 'No, not like that'), they persisted longer in enforcing the learned norms in the face of repeated non-conformity by the new actors. This finding suggests that not all generic, normative inferences are created equal, but rather they depend - at least for their strength - on the nature of the acquisition process.

Teaching versus enforcing game rules in preschoolers' peer interactions.

Children use normative language in two key contexts: when teaching others and when enforcing social norms. We presented pairs of 3- and 5-year-old peers (N=192) with a sorting game in two experimental conditions (in addition to a third baseline condition). In the teaching condition, one child was knowledgeable, whereas the other child was ignorant and so in need of instruction. In the enforcement condition, children learned conflicting rules so that each child was making mistakes from the other's point of view. When teaching rules to an ignorant partner, both age groups used generic normative language ("Bunnies go here"). When enforcing rules on a rule-breaking partner, 3-year-olds used normative utterances that were not generic and aimed at correcting individual behavior ("No, this goes there"), whereas 5-year-olds again used generic normative language, perhaps because they discerned that instruction was needed in this case as well. Young children normatively correct peers differently depending on their assessment of what their wayward partners need to bring them back into line.

The emergence of human prosociality: aligning with others through feelings, concerns, and norms.

The fact that humans cooperate with nonkin is something we take for granted, but this is an anomaly in the animal kingdom. Our species' ability to behave prosocially may be based on human-unique psychological mechanisms. We argue here that these mechanisms include the ability to care about the welfare of others (other-regarding concerns), to "feel into" others (empathy), and to understand, adhere to, and enforce social norms (normativity). We consider how these motivational, emotional, and normative substrates of prosociality develop in childhood and emerged in our evolutionary history. Moreover, we suggest that these three mechanisms all serve the critical function of aligning individuals with others: Empathy and other-regarding concerns align individuals with one another, and norms align individuals with their group. Such alignment allows us to engage in the kind of large-scale cooperation seen uniquely in humans.

Young children understand and defend the entitlements of others.

Human social life is structured by social norms creating both obligations and entitlements. Recent research has found that young children enforce simple obligations against norm violators by protesting. It is not known, however, whether they understand entitlements in the sense that they will actively object to a second party attempting to interfere in something that a third party is entitled to do-what we call counter-protest. In two studies, we found that 3-year-old children understand when a person is entitled to do something, and so they actively defend this person's entitlement against unjustified interference from second parties. In some cases, they even enforce second-order entitlements, for example, in the case of ownership where an owner is entitled to entitle others to use the owner's property.