Little is known about how processes underlying maternal psychopathology, such as emotion dysregulation (Edys), are related to children’s adjustment problems. Further, scant research has explored child protective factors that can buffer these associations. The present study used a multi-method approach to examine whether child positive affect (PA) can serve as a protective factor in the relations between mothers’ Edys and children’s adjustment problems. The sample included 96 mothers and their preschool-age children. Mothers’ Edys was assessed via self-report and physiological assessment. Child PA and adjustment problems were measured using maternal report. Child PA significantly moderated the relations between maternal physiological Edys and child internalizing and externalizing problems as well as between maternal self-reported Edys and child internalizing, but not externalizing, problems. These results suggest high PA can facilitate child adjustment in the context of low maternal Edys.