We examined whether children feel regret when their failure to make a prosocial choice negatively affects a peer. Five-to-six-year-olds and 7-to-9-year-olds played a game in which they completed a sticker sheet to win a prize. Children then decided whether to donate a spare sticker to another child; most children did not donate. Children discovered that the next child did not have enough stickers to win a prize, and rated their emotions. At this point, children did not know whether the next child could have been able to win the prize if they had donated the sticker in question. This counterfactual information was then provided, and children rated whether they felt happier, sadder, or the same as before. Only the 7-to-9-year-olds’ responses suggested that they experienced interpersonal regret. We also showed that experiencing interpersonal regret in the sticker task resulted in children making more prosocial choices in a separate task.