OBJECTIVE Safety information regarding the use of medication, over-the-counter drugs, and supplements for Japanese children is scarce. The aim of this study was to clarify adverse drug reaction (ADR) experiences in children and consider the method to collect ADRs efficiently. METHODS We conducted a questionnaire survey regarding the ADR experiences of 20,412 children who were attending a preschool or kindergarten in the cities of Warabi and Toda, Saitama Prefecture, in May 2013. RESULTS Responses were received from the guardians of 15,076 children (49.5% girls; 8.2 ± 3.5 yr). A total of 196 guardians (1.3%) responded that their children had experienced ADRs. Among them, a total of 243 suspected drugs and 284 ADRs were reported. Of the 243 suspected drugs, 2.5% were associated with a vaccine. The most frequently reported medication, reaction, and “medication–reaction pair” were antibacterials for systemic use, rash, and “antibacterials for systemic use and rash,” respectively. CONCLUSIONS In this study, we clarified that there were many potential ADRs among children, but all “medication–reaction pairs” reported were consistent with adverse events reported in the clinical trials available in the prescribing information of each medication. This study provides data respective to the frequency of these adverse events in the general pediatric population. Additional education is needed to enlighten guardians of the importance to report ADRs through the Direct Patient Reporting System.