Collaborative mother–toddler communication and theory of mind development at age 4

• The role of social pragmatics of communication in children's ToM is examined.
• Both mothers and toddlers engage in more collaborative communication acts.
• Both maternal and toddler support/confirming acts predict children's ToM.
• Toddlers' collaborative acts are unique and independent contribution to ToM.
• Actively co-constructed collaborative talks by both mother and toddler promotes ToM.

Focusing on social pragmatics, this longitudinal study investigated the contribution of mother–toddler collaborative communication to theory of mind (ToM) development at age 4. At age 2½, 78 toddlers (42 boys) and their mothers were observed during pretend play. At age 4, children were tested using 4 false belief understanding tasks. Both mothers and toddlers engaged in more collaborative (inform, guide/request, and support/confirm) than non-collaborative communication acts. Other-focused collaborative acts of support/confirm by mothers and toddlers predicted children's false belief understanding, even after controlling for 5 covariates. In addition, as active agents in their own ToM development, the contribution of toddlers' collaborative acts to false belief understanding was independent of their mother's. Finally, the way toddlers and their mothers co-constructed their communication mattered. Only when toddlers engaged in high levels of collaborative acts, the mothers' high levels of collaborative acts demonstrated a positive effect on children's ToM development. The applied implications of these findings are discussed.