In this paper, we offer a theoretical account of the emotion-cognition dialectic (i.e. the unit of feeling and cognition in thought) in identity formation (or identification), focusing on early childhood and mathematics. We consider how contradictory (emotional-cognitive) experiences which arise in different forms of mathematical activity (a mathematical play activity versus formal classroom mathematics) produce and are produced by contradictory acts of mathematical identification. We illustrate this perspective using the case of Daniel (aged 6 years) who expressed the emotion of 'astonishment' at seeing himself on video engaged in a play activity. We highlight how this experience of emotion-cognition enables Daniel to articulate a juxtaposition between play that is 'fun' and his classroom mathematics that makes him 'tired', which we associate with contrasting mathematical identifications. This recognises that social/cultural symbolic forms of emotion-cognition and identification are present in dialogue with others/adults even at this young age. We therefore, call for a research agenda that explores how such identifications might become sedimented into mathematical identities as the child develops.