In this longitudinal study, 52 typically developing preschoolers engaged in a hiding game with their mothers when children were 42-, 54-, and 66-months old. Children's understanding of mind, positive affect, and engagement with the task were rated, and mothers' utterances were coded for role and content. Analyses confirmed that some facets of children's understanding of mind developed sequentially; specifically, they expressed an understanding of knowledge access before an understanding of deception and false beliefs, and expressed an understanding of deception before an understanding of false beliefs. Children's understanding of mind increased across visits and positively correlated with false belief task performance. Results suggest that mothers may tailor the content of their utterances to the child's growing expertise, but the role of mothers' utterances did not change. Observing preschoolers engaged in a playful hiding game revealed that children's understanding of mind not only increased with age but also developed sequentially.