This study is a clinical trial, multicenter, controlled versus placebo whose main objective is to evaluate the efficacy of ondansetron to decrease the intensity of vomiting in children with acute gastroenteritis during winter emergencies Upon arrival to the emergency room after signing. Consent, an ECG is performed in eligible patients. Children meet all the criteria for inclusion and non-inclusion receive, at random, one of two treatments: ondansetron (active) or placebo. The study does not alter the usual care of the child to the emergency room. After passing emergency, patients will be followed in the study for 8 days, through a phone call home to J3 and J7. The total duration of patient participation in the study is 8 days, including 4 hours emergencies (usual transit time to emergencies).