ImportanceDeveloping core outcome sets is essential to ensure that results of clinical trials are comparable and useful. A number of core outcome sets in pediatrics have been published, but a comprehensive in-depth understanding of core outcome sets in this field is lacking.ObjectiveTo systematically identify core outcome sets in child health, collate the diseases to which core outcome sets have been applied, describe the methods used for development and stakeholder participation, and evaluate the methodological quality of existing core outcome sets.Evidence ReviewMEDLINE, SCOPUS, Cochrane Library, and CINAHL were searched using relevant search terms, such as clinical trials, core outcome, and children, along with relevant websites, such as Core Outcome Measures in Effectiveness Trials (COMET). Four researchers worked in teams of 2, performed literature screening and data extraction, and evaluated the methodological quality of core outcome sets using the Core Outcome Set–Standards for Development (COS-STAD).FindingsA total of 77 pediatric core outcome sets were identified, mainly developed by organizations or researchers in Europe, North America, and Australia and mostly from the UK (22 [29%]) and the US (22 [29%]). A total of 77 conditions were addressed; the most frequent International Classification of Diseases, 11th Revision category was diseases of the digestive system (14 [18%]). Most of the outcomes in pediatric core outcome sets were unordered (34 [44%]) or presented in custom classifications (29 [38%]). Core outcome sets used 1 or more of 8 development methods; the most frequent combination of methods was systematic review/literature review/scoping review, together with the Delphi approach and consensus for decision-making (10 [14%]). Among the 6 main types of stakeholders, clinical experts were the most frequently involved (74 [100%]), while industry representatives were rarely involved (4 [5%]). Only 6 core outcome sets (8%) met the 12 criteria of COS-STAD.Conclusions and RelevanceFuture quality of pediatric core outcome sets should be improved based on the standards proposed by the COMET initiative, while core outcome sets methodology and reporting standards should be extended to pediatric populations to help improve the quality of core outcome sets in child health. In addition, the COMET outcome taxonomy should also add items applicable to children.