BackgroundStudies suggest that group-based well child care—a shared medical appointment where families come together as a group to receive pediatric primary care—increases patient-reported satisfaction and adherence to recommended care. Evidence supporting the use of group well child care for mothers with opioid use disorder, however, is lacking. The overall objective of the Child Healthcare at MATER Pediatric Study (CHAMPS) trial is to evaluate a group model of well child care for mothers with opioid use disorder and their children.MethodsCHAMPS is a single-site 2-arm cluster randomized controlled trial. A total of 108 mother–child dyads will be enrolled into the study. Twenty-six clusters of approximately 4 mother-infant dyads each will be randomized 1:1 to one of two study arms (intervention or control). Clustering will be based on child’s month of birth. In the intervention arm, group well child care will be provided on-site at a maternal substance use disorder treatment program. Mother–child dyads in the control arm will receive individual well child care from one nearby pediatric primary care clinic. Dyads in both study arms will be followed prospectively for 18 months, and data will be compared between the two study arms. Primary outcomes include well child care quality and utilization, child health knowledge, and parenting quality.DiscussionThe CHAMPS trial will provide evidence to determine if a group well child care offered on-site at an opioid treatment program for pregnant and parenting women is beneficial over individual well child care for families impacted by maternal opioid use disorder.Trial registrationClinicalTrials.gov identifier: NCT05488379. Registered on Aug. 04, 2022.