Coparenting and children's temperament predict firstborns' cooperation in the care of an infant sibling

This study examined how coparenting and firstborn children's temperament predicted children's cooperative behavior in response to maternal requests for assistance in the care of a 1-month-old infant sibling. Children's cooperative responding was observed during a diaper change session for 216 firstborns (ages 13 to 70 months; M = 32). Parents also completed questionnaires assessing coparenting and children's temperament. Results suggested that coparenting quality moderated the association between children's temperament (i.e., soothability) and children's cooperation as revealed in a Temperament × Cooperative Coparenting × Undermining Coparenting interaction. Specifically, low soothability predicted low levels of children's cooperation in families with high undermining and low cooperative coparenting, over and above the effects of child age, gender, and mothers' education. Findings further our understanding of how temperamental characteristics and coparenting quality conjointly predict individual differences in firstborn children's positive adjustment across the transition to siblinghood.