Across two studies we explore how individual and dyadic factors influence children's (M[subscript age] = 61 months; 52% male; 55% White British) use of mental state talk (MST) with peers during shared play. Results from actor-partner interdependence modelling (APIM; n = 190 children) indicate that children's MST use is significantly linked to the MST use of their play partner but is unrelated to either their own or their play partner's theory-of-mind understanding. Furthermore, results from one-with-many (n = 87 children) modelling suggest there is little to no stability in children's use of MST across play partners or their tendency to elicit MST from different peer partners, cautioning against investigating MST with peers without considering features of the dyad within which interactions occur.