<p>While existing studies highlight the significance of mothers’ emotional abilities and family environment in shaping children’s callous-unemotional (CU) traits, few clarify the dynamic trajectories and reciprocal relationships among maternal emotional expressiveness (EE), family cohesion (FC), and children’s CU traits in Chinese families. To address existing gaps, this study examined the co-development processes among maternal positive and negative EE, FC, and children’s CU traits, with a focus on FC as a mediator of the bidirectional relationship between maternal EE and children’s CU traits. This study investigates 561 Chinese mothers with children aged 6–12 years across three time points, each separated by a 6-month interval. The results show bidirectional relationships between maternal negative EE and children’s CU traits from T2 to T3. However, maternal positive, rather than negative EE at T1, is negatively associated with children’s CU traits at T3 through FC at T2. Interestingly, children’s CU traits at T1 in turn are indirectly associated with maternal positive and negative EE at T3 via FC at T2. These findings imply a dynamic interplay between maternal EE and CU traits in children, while FC may ameliorate the adverse bidirectional spillover between them. Future prevention and intervention programs should prioritize enhancing maternal EE and FC, particularly in families with children exhibiting elevated CU traits.</p>