We use a multi-dimensional identity theory to examine how children's picturebooks present discourses about what mathematics is and what doing mathematics means. In our critical content analysis of twenty-four picturebooks, we found four recurring hidden messages that frame mathematical ability as preternatural; as having a magic eye; as doing calculations accurately and quickly; and as associated with social awkwardness. We explore the repercussions of such messages for learners at the earliest stages of their mathematical identity development. Ultimately, we argue that even stories that reject regressive stereotypes about gender and race may still reinforce other stereotypes that require critical examination.