Despite numerous studies of the development of theory of mind, how children express their understanding of mind in less structured, play settings has gone largely unstudied. Many developmental accounts, regardless of disagreement on other theoretical issues, agree that the child’s engagement within social contexts is crucial to the development of understanding of mind. Our goals were to collect a detailed account of how children use their understanding of mind and how mothers align their support to the child’s capabilities within social interactions. In this longitudinal study, typically developing preschoolers (N = 52) engaged in a hiding game with their mothers in a semi-structured play setting when the children were 42-, 54-, and 66-months old. Aspects of children’s understanding of mind were rated including understanding of knowledge access, deception, false belief, and emotional response to false belief, as well as, affective charge and engagement with the task. Mothers’ utterances were coded for various characteristics, particularly role and content. Children’s understanding of mind increased across visits and positively correlated with false belief task performance at the 42- and 54-month visits, r_s = .35 and .39, p < .05, but not the 66-month visit, r_s = –.25, p = .10. Children’s enthusiasm was positively related to their understanding of mind at the first and second visits, but not the last. Mothers tailored the content of their utterances to the child’s growing expertise, but whether mothers adjusted the role of their utterances to children’s understanding of mind remains unclear. Observing children’s playful use of their emerging understanding of mind in social interactions allowed for the capture of subtle variations in how children express and caregivers support their understanding.

INDEX WORDS: Understanding of mind, Theory of mind, False belief understanding, Maternal scaffolding, Social interactions, Longitudinal, Preschoolers