The development of third-party intervention in children aged 4-10: Balancing unfairness aversion and self-interest

This study explored how children (N = 196, ages 4-10) balance fairness and self-interest when making costly third-party interventions. Using a third-party trust game, children made decisions in both punishment and compensation contexts across three degrees of unfairness. Dynamic time warping (DTW)clustering was applied to identify distinct intervention patterns across unfairness conditions, offering a novel approach to capture children's fairness behaviors as coherent trajectories rather than isolated responses. Results revealed that 4-year-olds, in low unfairness conditions (i.e., a 6:4 distribution), displayed more interventions than 10-year-olds, often exceeding what was required to restore fairness, whereas older children's interventions were more aligned with fairness demands. In low unfairness conditions, inhibitory control was positively associated with intervention intensity, though this effect weakened with age. Age-related differences were evident in the strategies employed, particularly in punishment contexts. Younger children tended to display less clear strategies, while older children were more likely to exhibit either fairness-oriented or self-interest-oriented strategies. Negative empathy-empathy for others' negative emotions-was positively associated with fairness-oriented decisions in punishment situations, with children exhibiting higher negative empathy more likely to be fair. However, the relationship between empathy and third-party compensation was less clear, as empathy was not significantly related to whether participants performed fairness- or self-interest-oriented behaviors. These findings suggest that with age, children's third-party intervention strategies become more context-sensitive, shifting from spontaneous punishment in mild unfairness toward more calculated, fairness- or self-interest-oriented decisions. By contrast, third-party compensation appeared to be relatively unaffected by age in terms of orientation.