Initial interactions matter: Warm-up play affects 2-year-olds' cooperative ability with an unfamiliar same-aged peer.

Interaction quality during cooperative exchanges affects children's ability to successfully coordinate their actions with a same-aged peer to attain a shared goal. However, it is unclear how initial interactions in one context shape children's ability to cooperate in a subsequent task. In the current research, we examined whether the interaction quality (e.g., affiliation, antagonism, joint coordinated engagement, joint contribution) of a warm-up period between 2-year-old unfamiliar dyads (N = 144 dyads) predicts the dyad's performance and interaction quality in a following cooperative task. Children who participated more effectively during a toy clean-up activity at the end of the warm-up interaction were more likely to respond to their partner's efforts to cooperate in the novel cooperative task. Initial displays of affiliation during the warm-up period appeared to enhance cooperative ability by facilitating cooperative motivation. The current research demonstrates that initial interactions influence toddlers' cooperative performance and thus highlights the importance of considering task order and children's social behaviors when designing studies on cooperative competence.