The objective of this study was to examine associations between patient age and medication errors among pediatric inpatients. Secondary analysis of data sets generated from 2 tertiary pediatric hospitals: (1) prescribing errors identified from chart reviews for patients on 9 general wards at hospital A during April 22 to July 10, 2016, June 20 to September 20, 2017, and June 20 to September 30, 2020; prescribing errors from 5 wards at hospital B in the same periods and (2) medication administration errors assessed by direct prospective observation of 5137 administrations on 9 wards at hospital A. Multilevel models examined the association between patient age and medication errors. Age was modeled using restricted cubic splines to allow for nonlinearity. Prescribing errors increased nonlinearly with patient age (P = .01), showing little association from ages 0 to 3 years and then increasing with age until around 10 years and remaining constant through the teenage years. Administration errors increased with patient age, with no association from 0 to around 8 years and then a steady rise with increasing age (P = .03). The association differed by route: linear for oral, no association for intravenous infusions, and U-shaped for intravenous injections. Older age is an unrecognized risk factor for medication error on general wards in pediatric hospitals. Contributors to risk may be the clinical profiles of these older children or the general level of attention paid to medication practices for this group. Further investigation may allow the design of more targeted interventions to reduce errors.