ADHD; AhR; BMI; Cd; Child behaviour; DDT; DF; Dioxin-like compounds; FLEHS; Flemish Environment and Health Study; GC-MS; HCB; HR-ICP-MS; Heavy metals; High Resolution Inductively Coupled Mass Spectrometry; IQR; LOD; LOQ; OR; PCB; SDQ; aryl hydrocarbon receptor; attention deficit/hyperactivity disorder; body mass index; cadmium; dichlorodiphenyltrichloroethane; dilution-factor; gas chromatography with mass spectrometric detector; hexachlorobenzene; interquartile range; limit of detection; limit of quantification; odds ratio; p,p'-DDE; para,para-dichlorodiphenyldichloroethylene; polychlorinated biphenyls; strengths and difficulties questionnaire