In contrast with a classic view that young children select friends based simply on physical proximity, young children's choice of friends might be closely related to their self-cognition and cognition of friends. To reveal this question in this study, I review research of young children concerning three themes: cognition of self and friends, friendship choice, and social comparison. First, I focus on young children's cognition of self and friends, especially on self-evaluation and their evaluation of friend's ability. Second, I describe how friendship is related to cognition of self and friends, referring to studies of friendship and choice of friends in early childhood. Third, in respect of the social comparison processes and self-evaluation maintenance models, I discuss the features of young children's self- and friend-cognition. The review of related research suggests that young children might compare the ability of themselves with those of other children, and choose friends on the basis of the comparison.