Hospitalized children may be particularly vulnerable to medication errors given differences in dosing and monitoring of medications. This study, conducted at five California children's hospitals, used several medication error detection methods to characterize the frequency and types of medication errors in this population. Overall, errors requiring pharmacy intervention occurred at a rate comparable to prior studies, but more errors were detected by using a previously validated trigger tool than by standard voluntary incident reporting. The inability of incident reporting to detect medication errors has been documented in prior research.