This study used a family systems framework to examine associations between parent-child synchrony, interparental relationship satisfaction, and children's emotion regulation. The sample included 75 families from socioeconomically and ethnically diverse backgrounds who had a child between 18 and 27 months (Mage = 20.9 months). Mothers and fathers from the same families completed separate visits with their child. Mother-child and father-child synchrony (i.e., the extent to which dyads displayed a contingent pattern of communication) were coded from observations of parent-child teaching tasks completed individually with their child. Children's emotion regulation was coded from observations of a brief frustration task and included codes for children's emotional distress and adaptive coping (i.e., task-focused coping strategies). Results from dyadic path models demonstrated that father-child, but not mother-child, synchrony was associated with less distress in toddlers, and that fathers’ self-reported interparental relationship satisfaction was negatively associated with toddlers’ coping. The final model revealed that mothers’ relationship satisfaction moderated associations between both mother-child and father-child synchrony and toddlers’ adaptive coping. Further, fathers’ relationship satisfaction moderated the association between father-child synchrony and toddlers’ distress. These results suggest that the quality of father-child interactions play a unique and important role in supporting children's emotion regulation in challenging situations, and that interparental relationship satisfaction is a key factor to consider. Further, this work highlights the importance of considering the entire family system, such as how interactions between parents indirectly influence children's development.