Little is known about the flexibility of children's prosocial motivation. Here, 2‐ and 3‐year‐old children's (n = 128) internal arousal, as measured via changes in pupil dilation, was increased after they accidentally harmed a victim but were unable to repair the harm. If they were able to repair (or if they themselves did not cause the harm and the help was provided by someone else) their arousal subsided. This suggests that children are especially motivated to help those whom they have harmed, perhaps out of a sense of guilt and a desire to reconcile with them. Young children care not only about the well‐being of others but also about the relationship they have with those who depend on their help.