This study examined the associations between perceived and observed coparenting and toddlers' adaptive functioning. Seventy-seven typically developing toddlers aged between 21 and 27 months and their biological parents residing in Ireland participated in the study. Participating families were Caucasian and English speaking. Parents' perceived coparental relationship was assessed via self-report. In addition, coparenting dynamics were observed during triadic free-play and structured-play tasks. Mothers reported on their toddlers' adaptive functioning. Results indicated a negative association between undermining coparenting and toddlers' social and communication adaptive skills. Findings from the current study highlight the critical role played by triadic family processes in young children's development.