Instances of altruism in children are well documented. However, the underlying mechanisms of such altruistic behavior are still under considerable debate. While some claim that altruistic acts occur automatically and spontaneously, others argue that they require behavioral control. This study focuses on the mechanisms that give rise to prosocial decisions such as sharing and costly punishment. In two studies it is shown in 124 children aged 6–9 years that behavioral control plays a critical role for both prosocial decisions and costly punishment. Specifically, the studies assess the influence of taxing aspects of self‐regulation, such as behavioral control (Study 1) and emotion regulation (Study 2) on subsequent decisions in a Dictator and an Ultimatum Game. Further, children's perception of fairness norms and emotional experience were measured. Taxing children's behavioral control prior to making their decisions reduced sharing and costly punishment of unfair offers, without changing perception of fairness norms or the emotional experience. Conversely, taxing children's emotion regulation prior to making their decisions only led to increased experience of anger at seeing unfair offers, but left sharing, costly punishment and the perception of fairness norms unchanged. These findings stress the critical role of behavioral control in prosocial giving and costly punishment in childhood. This study establishes a functional role for behavioral control in altruistic decisions in childhood. After taxing behavioral control children became less altruistic as indicated by a decrease in sharing and an increase in accepting unfair offers. A control experiment that taxed children’s emotion regulation before making their decision showed no such effect. The results carve out a special role for a specific behavioral control mechanism in altruistic decisions during childhood.