Flexible social attention, including visually attending to social interaction partners, coupled with positive affect may facilitate adaptive social functioning. However, most research assessing social attention relies on static computer-based paradigms, overlooking the dynamics of social interactions and limiting understanding of individual differences in the deployment of naturalistic attention. The current study used mobile eye-tracking to examine relations between social attention, expressed affect, and behavioral inhibition during naturalistic play in young children. Children (N = 28, M[subscript age] = 6.12, 46.4% girls, 92.9% White) participated in a 5-min free play with a novel age- and sex-matched peer while mobile eye-tracking data were collected. Interactions were coded for social attention and expressed affect and modeled second-by-second, generating 4,399 observations. Children spent more time dwelling on toys than on peers or anywhere else in the room. Further analyses demonstrated children were almost twice as likely to gaze at their peer when simultaneously self-expressing positive affect. Additionally, children were more than twice as likely and more than three times as likely to self-express positive affect when dwelling on peer or in the presence of peer-expressed positive affect, respectively. Behavioral inhibition was not significantly related to social attention. However, children higher in behavioral inhibition were less likely to self-express positive affect in the presence of peer-expressed positive affect. The current results provide a snapshot of relations between social attention, expressed affect and individual differences during play and provide guidance for future work assessing the roles of social attention and positive affect in facilitating positive social interactions.