The capacity to take another’s perspective appears to be present from early in life, with young infants ostensibly able to predict others’ behaviour even when the self and other perspective are at odds. Yet, infants’ abilities are difficult to reconcile with the well-known problems that older children have with ignoring their own perspective. Here we show that it is the development of the self-perspective, at around 18 months, that creates a perspective conflict between self and other during a non-verbal perspective-tracking scenario. Using mirror self-recognition as a measure of self-awareness and pupil dilation to index conflict processing, our results show that mirror recognisers perceive greater conflict during action anticipation, specifically in a high inhibitory demand condition, in which conflict between self and other should be particularly salient.