Human cooperation and group living are based on societies in which individuals not only care about their own interests but share common norms and values – such as morality and prosocial behavior. As early as the 18th century, Immanuel Kant postulated autonomy as the key to human morality. Kant explained that a rational agent with a free will would necessarily make moral – not immoral – decisions. However, the fundamental question of how moral behavior acquires normative weight remains unresolved until (...) the present day, especially when moral behavior entails personal costs for the individual. This dissertation builds on Kant’s thesis and aims to investigate important building blocks of moral autonomy at preschool age. Therefore, children’s own prosocial decisions as well as their normative and descriptive expectations about others’ prosocial actions are assessed and linked to fundamental underlying mechanisms such as cultural learning and collective intentionality. Study 1 assessed whether preschoolers enforce agreed-upon prosocial ver-sus selfish sharing norms in a group dictator game. Three- and 5-year-old children and two hand puppets had the opportunity to agree on how to distribute re-sources between themselves and a group of passive recipients. The findings sug-gest that preschoolers understand prosocial, but not selfish, agreements as binding even though prosocial sharing norms are associated with personal costs. Study Set 2 assessed in two experiments whether observed choice increases the children’s own prosocial sharing behavior. In Experiment 1, children observed an adult model who was provided with costly choice, non-costly choice, or no choice. As a next step, children were given the opportunity to decide how many stickers they would like to share with a sad animal puppet. Experiment 2 aimed to investigate possible age effects. The study design was reduced to condition and, a second test trial was added. Taken together, the results of Study Set 2 suggest that 5-year-old’s prosocial sharing behavior increases when previously having observed someone who intentionally acts prosocially at a personal cost. Study 3 investigated preschoolers’ descriptive expectations about the causal agent of prosocial and selfish actions, based on agents’ prior history of voluntary versus involuntary prosocial behavior. The results show that children at the age of 5.5 years use information about the circumstances and intentions of previous actions to generate descriptive expectations about other’s future prosocial behavior. From 4 years of age, children distinguish between an agent who shares voluntarily and an agent who shares only involuntarily. Taken together, this dissertation shows that preschool aged children infer and enforce prosocial – but not selfish – sharing norms. They engage in prosocial sharing which is affected by observed choice and they form descriptive expectations about others tendency to behave prosocial or selfish on the base of knowledge about the agents prosocial versus selfish intentions. (shrink)