•7–9-year-olds demonstrate interpersonal regret in a prosocial risk taking task.•Few 7–9-year-olds are prepared to take a prosocial risk.•Prosocial risk takers are more likely to experience interpersonal regret. Numerous studies have examined the development of regret about choices yielding non-optimal outcomes for the self (intrapersonal regret), but regret can also be experienced when one’s choices lead to poor outcomes for another person (interpersonal regret). We investigated interpersonal regret in children using a novel prosocial risk taking task that closely resembled in structure those used in intrapersonal regret studies. Children chose between two gambles to win a prize for themselves and a peer. In interpersonal trials, acting prosocially required children to incur a risk of winning nothing in order to improve the possible outcomes for another child. Regardless of their choice, children found out that the other child would have had a better outcome if they had chosen differently. Intrapersonal regret trials were also included where the participant themselves received a poor outcome that would have been better if a different choice had been made. Few children of 7-9-years were willing to take a personal risk in order to be prosocial. Those who did choose to take a prosocial risk were more likely to experience interpersonal regret than those who made the non-prosocial choice. There was no association between interpersonal and intrapersonal regret, potentially suggesting that different factors underlie their emergence, with interpersonal regret being prosocially motivated.