Happily egocentric: the impact of mood on children's mentalising, an exploratory study.

Relying on one's own egocentric knowledge to predict others' behaviour can lead to conflict. In adults, incidental happiness increases egocentric biases. This study was the first investigation of whether this is true for children. Younger (N = 90; aged 3 to 4.5), and older children (N = 75; aged 6to 7) watched short videos to induce happy or neutral mood. They then completed an age-appropriate false belief task. Younger children in the happiness condition were more likely to fail the task (Φ = .25), consistent with acting more egocentrically. The induction video did not affect older children's performance; however, those who self-reported a happier mood showed more egocentric bias (r = .43). Our exploratory study suggests that, like adults, happier children appear more egocentric in their mentalising. Future work is needed, with larger sample sizes and to understand whether the differences across age groups reflect a genuinely age-related change, or an artefact of the mood manipulation used.