ObjectiveThe current study examined how parental relationship changes were linked to observed parenting behaviors, parental depressive symptoms, and 3‐year‐old children's social–emotional development.BackgroundParental relationship changes may present risks to young children's well‐being. The specific processes linking these changes to child development, however, remain unclear because these changes are often confounded with other family risks. We applied an adapted family stress model to identify family‐based pathways conferring risk to children among predominantly low‐income unmarried families.MethodData are from 2,575 families who participated in the Building Strong Families study, which included primarily unmarried, low‐income couples transitioning to parenthood. Parental relationship changes were measured as overall changes in parents' romantic relationship status with each other and with new partners and multipartner fertility. Structural equation models (SEM) were estimated to link these changes directly and indirectly, via mothers' and fathers' parenting behaviors and depressive symptoms, to children's behavior problems and effortful control.ResultsParental relationship changes were directly associated with paternal depressive symptoms and children's internalizing behaviors. Mothers' and fathers' parenting behaviors were independently associated with children's behavior problems and effortful control.ConclusionThe findings point to the value of simultaneously considering the observed parenting behaviors and depressive symptoms of mothers and fathers within the context of parent relationship changes.ImplicationsInterventions aimed at strengthening low‐income unmarried families should focus on the quality of mothers' and fathers' parenting to bolster young children's development because these parenting behaviors were more closely associated with child development than were parental relationship changes.