Many studies have examined associations between children's theory of mind and social behavior with familiar peers, but to date none have examined how theory of mind might relate to behavior toward unfamiliar peers in a play setting. Forty-four 4-year-olds (21 girls, 23 boys) participated in standard theory-of-mind tasks and in a play session with 3 or 4 other children who were unfamiliar. Children were also tested on general vocabulary ability. No relations were found between theory of mind and social engagement. However, positive associations were found between theory of mind and time spent observing, but not interacting with, other children. Possible explanations of the links between theory of mind, temperament, and social interest are considered.