This study investigated the extent to which 7-year-olds engage in the negative aspects of cooperation from two perspectives. Experiment 1 revealed that although 7-year-olds did not initiatively break rules, they passively violated rules by failing to tattle on adult players in a collaborative situation. Experiment 2 revealed that, although children tended to altruistically accept violations by their partner, their cooperation was limited when they received a high reward. These results suggest that cooperation is more important than conforming rules for children, although both cooperation and conforming to rules are also crucial.

In our experiment, children rarely actively cheated regardless of the differences between conditions. They did not actively break the rules, suggesting that they understood the rules and intended to follow them. Considering that a previous study reported that 70–90% of 6- to 7-year-olds cheated in the peeking paradigm when they participated alone19, the adult players in our study might function as an effective monitor for children. Our result is consistent with findings that cheating behavior in 5- and 8-year-olds decreased14 and 5-year-olds stole less when they were monitored by another person23. These prior findings suggest that the presence of others did not induce active violations by children, but inhibited them. On the other hand, the 7-year-olds in our study accepted violations by not tattling in collaborative situations. That is, children who collaborated with the adult partner tended to show more negative aspects of cooperation relative to those who individually participated in the quiz, suggesting that a child’s tendency to deliberate between cooperation and conforming to rules is fragile and likely influenced by their partnerships with others. The children in our study did not initiate violations but accepted them whenever the adult partner did, suggesting that cooperation in collaborative situations may be more important as opposed to following rules to them.

Since Gräfenhain, et al.15 revealed that the tattling behavior of 3-year-olds did not change depending on whether the child and the adult player were collaborating15, developmental changes from ages 3 to 6 might exist to explain negative aspects of cooperation in collaboration. For example, it is possible that the development of negative aspects of collaboration is influenced by the recognition of how group members behave. Plötner, Over, Carpenter & Tomasello24 reported that 5-year-olds thought that collaborative members should help each other24. Actually, 5-year-olds (but not 3.5-year-olds) chose to help collaborative partners rather than non-collaborators25. Thus, perhaps the children in the collaborative condition of the present study thought that they should help their partner and chose to keep their partner’s cheating secret. At the same time, the children’s recognition of in-group members also changed, such that 5-year-olds (but not 3.5-year-olds) chose to help in-group members rather than out-group members25. In addition, Jordan et al.12 found that 6-year-olds punished a dictator more in a dictator game when an out-group member decided to share unequally with an in-group member than the reverse12. In Experiment 1, when the child and the adult player collaboratively participated in the quiz, the adult player resembled an in-group member because they were on the same team. Conversely, when the child and the adult player participated in the quiz individually, the adult player resembled an out-group member because they were irrelevant. As a result, it is possible that children prioritize cooperation in the collaborative condition. This result could also be based upon reputation management, since even 5-year-olds are more concerned about their reputation as an in-group member than an out-group member26. Even though it is unclear how children regard adult players, recognition of how group members behave seems to affect children’s behavior.

The second possibility for the development of negative aspects of cooperation is the development of a child’s ability to calculate loss and gain. In third-party punishment, 6-year-olds, unlike 5-year-olds, can decide to give punishment based upon its cost27. When the child and the adult player are on the same team, the partner’s cheating profited the children in comparison to when they individually participated in the quiz. Thus, the ability to calculate loss and gain is critical for the negative aspects of cooperation.

When children participated in the quiz with their partner on the same team, they tended to avoid tattling even when cheating did not affect their reward, suggesting that 7-year-olds altruistically follow violations for their team member. However, this tendency is limited when rewards are kept at a high level. When a child’s reward was fixed at a lower level, their degree of cooperation with the partner resembled the degree of cooperation that occurred when the child and the adult player individually participated in quizzes. This result corresponds to the adult data in a prior study by Gino & Pierce21. According to Gino & Pierce21, this difference in behavior results from a modification in the degree of emotional distress caused by an inequality in the reward. Recent developmental studies have revealed that children are sensitive to inequality. Fehr, Bernhard & Rockenbach28 reported that 3- to 8-year-olds prefer equal distribution over unequal distribution, and this tendency intensifies with age28. Seven-year-olds start to care not only about unequal distribution, in which they are given smaller reward, but also unequal distribution, where they are given bigger rewards22. Thus, it is possible that the children tried to decrease the emotional distress caused by inequality by keeping their partner’s cheating secret when the reward exceeded their partner’s reward.

Furthermore, altruistic cheating in adults may occur because violations are verified by profiting over other persons or groups9,17,18. Even though breaking rules is not good, their violations may be perceived as being lighter than they actually are or are rationalized because another person or group is profiting. Although we did not confirm this possibility in our study, perhaps this psychological mechanism allows children to altruistically engage in the negative aspects of cooperation.

Our study has three main limitations. First, we did not manipulate the partner’s characteristics and the partner was always an adult. Since children typically look up to adults as role models and because they are obviously physically superior to children, there was not an equal relationship between partner and child. Additionally, because the adult partner was always in the room during the experiment, there was no opportunity for the children to tattle without being noticed by their partner. Thus, this setting might inhibit children’s active cheating or tattling because they fear revenge from the adult players29. Therefore, future work will examine children’s negative aspects of cooperation based on the different ages or attributes of their collaborative partners, such as peers30.

Second, we failed to adequately address developmental changes in terms of the negative aspects of cooperation. Although 3-year-olds’ tattling behavior did not reflect the degree to which the child and the partner were collaborating15, our study revealed that 7-year-olds changed their behavior. What developmental changes occur from ages 3 to 6 must also be examined. Berndt31 reported children tend to engage in more anti-social behavior as they grow, peaking around age 1531. Thus, examining developmental changes after children reach the age of seven may be fruitful. Furthermore, adults exhibited altruistic cheating even when the reward to the participant was fixed at a low level, even though the degree of this occurrence was low7. The processes underlying the development of altruistic cheating and its relationship with cognitive ability are additional future research topics.

Lastly, the effects of children’s background are in need of examination. First, previous studies revealed differences in the evaluations of blue lies between Asian and Western cultures. In detail, unlike Chinese children, Canadian children have been found to evaluate lies for self-interest more positively than lies for group-interest32. This difference may be derived from group-oriented Chinese cultural values, whereas Canadian culture is more individually-oriented. Considering these results, Western children might engage in fewer negative aspects of cooperation relative to Asian children. Thus, the effect of cultural values on the negative aspects of cooperation is an area ripe for future research. Second, it is important to examine the effect of SES on negative aspects of cooperation in children since previous studies have reported that SES affects children’s altruistic behavior, although these results reveal a trend that is inconsistent across studies33,34,35.

In sum, this study provided evidence that collaboration promotes the engagement of 7-year-olds in negative aspects of cooperation. Importantly, they engaged in negative aspects of collaboration not by actively creating them but by accepting the violations of others. Children also engaged in altruistic cheating for their partner, particularly when their reward was secured at a high level. Our findings suggest that, although 7-year-olds tend to believe that cooperating is more important than following rules when both are compatible, they behave strategically depending on the situation at hand. Although many studies reveal the positive aspects of cooperation in children, our study provides a novel viewpoint regarding the negative aspects of cooperation and its development.