Background: Acute gastroenteritis is one of the most common causes of dehydration in children. Parents’ education is an essential part of its management. In this study, we assessed the efficacy of discharge instructions in the pediatric emergency department for parents of children with acute gastroenteritis, together with disease prognosis and parents’ satisfaction. Methods: An observational prospective cohort study was conducted among parents of children with acute gastroenteritis, with mild-to-moderate dehydration, who presented to the pediatric emergency room from March 2018 to July 2018. Parents were interviewed upon their child’s presentation and in follow-up phone calls after one week to assess the parents’ knowledge and the disease’s prognosis. Results: There were a total of 218 parents of children with acute gastroenteritis of mild and moderate dehydration. The mean age was four years and one month ± three years and seven months. Forty-four percent of study participants had reasonable awareness of their child’s condition, and most patients (86%) improved fully. The exact adherence to instructions was 54%, the proportion of children who returned to the emergency department was 13%, and parental satisfaction and appreciation of the provided education was 98%. Conclusion: In the study group, not strictly following fluid rehydration plans in discharge instructions did not negatively affect the course of improvement. This indicates that simple instructions to rehydrate with any fluid a child might accept and give clear red flags for observation are likely to be enough to treat gastroenteritis of mild-to-moderate severity.