In this longitudinal study, we explored children's reasoning about social inclusion/exclusion at Year 1 and Year 3 (n = 169 Year 1, n = 129 Year 3) of early primary education in Australia and how this reasoning related to changes in children's epistemic cognition. The data collection involved 30-minute interviews in which children were asked to engage in two tasks related to (1) epistemic cognition and (2) including an aggressive child in play. Findings showed that children were more likely to choose to include the aggressive child in Year 3 if they also expressed Subjectivist epistemic beliefs than if they expressed Objectivist beliefs. The children who expressed Subjectivist epistemic beliefs were more likely to justify their decision to include an aggressive child in a more nuanced and complex manner. We argue for a focus on epistemic reflexivity for reasoning about social inclusion as a way in which to provide new understandings about how broader contextual influences may mediate such reasoning.