Background: As an important aspect of health and development, a number of policy and practice initiatives across education, health and social care are aimed at increasing children's emotional wellbeing. Links have been made between young children's emotional wellbeing and play although empirical evidence is limited. This paper demonstrates that when children perceive an activity as play, they show more signs of emotional wellbeing than when they perceive the same activity as not play. Method: 129 children aged between 3 and 5 years participated in the study. The cues children use to differentiate play and not play were used to create an activity session that was 'like play' and an activity session that was 'not like play'. The activity itself remained constant. Children were allocated to either of the activity session types alternately and emotional wellbeing was measured using the Leuvens Involvement Scale (Laevers, Vandenbussche, Kog, and Depondt, 1994). Results: There was a significant difference in the level of emotional wellbeing displayed by children in the two activity session types. Children who undertook the 'like play' activity scored significantly higher than children who undertook the same activity but 'not like play'. Detailed observational analysis also showed increased behavioural indicators relating to emotional wellbeing amongst children participating in the 'like play' rather than 'not like play' activity session. Conclusion: Children demonstrate increased emotional wellbeing when they perceive an activity as play rather than not play. Findings support the proposition that play can be seen as an observable behaviour but also as a mental state. As well as providing important evidence as to the value of play for enhancing children's emotional wellbeing, findings are discussed in relation to professional practice in children's services. The paper highlights the training needs of practitioners to enable them to understand children's views about play and use this information to create playful situations which maximise the developmental potential of play.