Abstract: Third-party intervention plays a critical role in maintaining large-scale human group cooperation. Previous studies on children’s third-party intervention mainly focused on explicit norm violations, such as unfair distribution or damage to others’ belongings. Different from explicit violations, free-riding in group cooperation, where an individual benefits from others' contributions without incurring the corresponding costs) involves implicit norms and lacks clearly identifiable victims. Recognizing and addressing free riders in group cooperation from a third-party perspective is an important aspect of children’s social norms acquisition and the development of cooperative behavior. This study examined the development and motivations of third-party intervention preference among children aged 4 to 11 years old in scenarios involving group cooperation norms violations.
=In Study 1, 141 children (70 boys, Age range: 4.06~11.96 years, M_age = 8.02, SD = 2.30) heard a cooperation story in which one group member shirked effort by playing football instead of helping clean the classroom but still shared in the reward. Children’s moral evaluation, anger toward free-riding behavior, and their intervention preferences were measured in sequence. In Study 2, 125 children (63 boys, Age range: 4.34~11.68 years, M_age = 8.01, SD = 2.31) completed a similar task involving materials contribution to a collective resource. To test cross-situational stability and rule out majority-influence effects, the group composition was adjusted to two cooperators and two free riders. In this story, a four-member group jointly dropped gold coins into a magic jar to get more gold coins. Among them, two members of the group each dropped one gold coin into the magic jar, while the other two members did not. In the end, the two coins that were dropped into the magic jar turned into four gold coins, and then each member of the group received one gold coin. Similarly to Study 1, children’s moral evaluation, anger feeling on free-riding behavior, intervention preferences and motivations were measured.
Across both studies, children consistently evaluated free-riding negatively and reported anger toward it. As third-parties, children preferred intervention in free-riding behavior over non-intervention across all ages. With age, children’s preferences for third-party intervention showed a cross-situational stable developmental trend, gradually shifting from rewarding cooperators to punishing free riders. Importantly, the shift occurred earlier in effort-based scenarios (ages 5.51~5.67) than in material-based scenarios (ages 8.21~8.22). In terms of the motivations of intervention preferences, Study 2 found that the internal motivations for children to reward cooperators reflect both deontological motivation and consequentialist motivation. In contrast, the motivation to punish free-riders changes with age, gradually shifting toward the consequentialist motivation after age six. These findings indicated that the underlying motivations driving children’s intervention preferences are both specific and age-dependent.
These findings demonstrate that even young children can morally evaluate norm violations in group cooperation and engage in third-party interventions. Their intervention preferences develop in a stable, cross-situational manner, gradually shifting from rewarding prosocial behavior to punishing norm violators. However, the motivations underlying reward and punishment are distinct and age-dependent. This research provides valuable insights into the development of children’s cooperative behavior and their understanding of group cooperation norm.

Key words: group cooperation, norm violation, third-party intervention, internal motivation