Bathing Beaches; Cystic Fibrosis/rehabilitation; Holidays; Rehabilitation Centers/organization & administration; Child; Child, Preschool; Cystic Fibrosis/classification; Cystic Fibrosis/complications; Dyspnea/etiology; Dyspnea/prevention & control; Female; France; Growth Disorders/etiology; Growth Disorders/prevention & control; Health Promotion/organization & administration; Humans; Leisure Activities; Length of Stay/statistics & numerical data; Leukocytosis/etiology; Leukocytosis/prevention & control; Male; Play and Playthings; Program Evaluation; Seasons; Seawater; Severity of Illness Index; Time Factors; Weight Gain