More and more grandparents are involved in parenting and share the responsibility of raising children with parents in China. Less is known, however, regarding the mutual effects of caregivers on children in intergenerational coparenting families. This study aimed to examine how mothers’ and grandmothers’ self-control, mother-grandmother coparenting relationships, and caregiver-child attachment were associated and to investigate whether the pathways were different in mother-child and grandmother-child dyads. Participants were mothers and grandmothers from 501 intergenerational coparenting households. The results from Actor-Partner Interdependence Mediation Modeling (APIMeM) indicated that mothers’ and grandmothers’ self-control were indirectly related to their own caregiver-child attachment through their self-report coparenting relationships. Additionally, the effect of mothers’ self-control spilled over to the grandmother-child attachment through grandmothers’ self-report coparenting relationships. Overall, the findings indicated that mothers’ and grandmothers’ self-control, mother-grandmother coparenting relationships, and their attachment to the child significantly differed between mother-child dyads and grandmother-child dyads. This study contributes to a deeper understanding of women caregiver-child attachment processes and highlight the implications of using the dyadic approach in understanding and improving family functioning in intergenerational coparenting families, which provide implications for family interventions.