Does promising facilitate children's delay of gratification in interdependent contexts?

For cooperation to succeed, individuals must often 'delay gratification' and forego an immediate reward for a larger delayed reward that is co-produced through the cooperative act. This experiment asked whether a promise to wait increased children's propensity to coordinate with their partner by waiting to eat their own treat. In this first cooperative marshmallow test conducted online, 5- to 6-year-old UK-based children (n = 66) interacted from their homes via video call with a confederate child who either promised not to eat his treat (promise condition) or expressed the possibility that he might eat his treat (social risk condition). Across the full dataset and a reduced dataset in which participants were not accidentally interrupted during the task (n = 48), children in the promise condition waited longer to eat their treat than children in the social risk condition. Younger children, but not older children, also successfully delayed gratification more often in the promise condition than in the social risk condition. Thus, even when communication is one-sided in an interdependent marshmallow task, explicit promises can support children's motivation to delay gratification relative to explicit uncertainty.