Peer initiative refers to a child’s personal characteristic relevant to instigating play with peers, and it can be classified as friendly or unfriendly. This study used structural equation modeling to examine the contributions of mother’s coaching competence, parenting behavior, and child self-regulation to peer initiative. Participants comprised mothers of children aged 3 to 5 years (n = 343) in Korea and their teachers (n = 39). Structural equation modeling indicated that the relationship between mothers’ coaching competence and friendly peer initiative was fully mediated by maternal affection and child self-regulation. Furthermore, the relationship between mothers’ coaching competence and unfriendly peer initiative was partially mediated by maternal rejection and child self-regulation. These findings highlight the importance of children’s self-regulation for their social and adaptive development in a Korean cultural context and emphasize the need of maternal affection, which is reinforced by higher coaching competence, required for mothers. It is also worth noting that this study was conducted with a cultural group that collectivism and communality are highly valued.