Since a very young age, the majority of human social interactions involve objects. In these interactions, children seem to take into account who owns what. The notion of ownership thus does not involve only a person and an object, but is a relationship between several persons with respect to an object. This relationship is organized by a set of rules or property rights. Our work deals with children’s understanding of the notion of ownership. At what age do children acquire the understanding of property rights? Before an explicit mastery of the notion of ownership, do children have a more implicit understanding of it? More precisely, we explored the understanding and evaluation of illegitimate and legitimate transfers of property in children from 5 months to 5 years of age. We studied two types of ownership transgressions: illegitimate acquisition of an object (without owner’s intention to transfer it), and absence of restitution of an object to its owner. In all our studies, we presented to children property transfers between two characters using non-verbal animated cartoons or movies with puppets as actors, and then measured children’s understanding and evaluation of those transfers. The studies in Chapter 2 (Studies 1 and 2) assessed children’s evaluation of different modes of acquisition of an object. The two experiments of Study 1 explored 3- and 5-year-olds’s understanding and evaluation of illegitimate and legitimate property transfers. Adults were also tested as a control population. This study is the first one to investigate simultaneously children’s explicit and implicit understanding of the notion of ownership, by asking questions about property rights, as well as social and moral evaluations of the characters implicated in the transfers, respectively. In Study 1a, participants saw a character acquiring an object either in an illegitimate way (theft condition) or in a legitimate one (gift-reception condition). In Study 1b, an illegitimate action (theft) was compared to a legitimate action (giving). 5-year-old children (as adults) showed both an implicit understanding of ownership through their social/moral evaluation (preferring the legitimate agent (gift recipient or giver) compared to the illegitimate agent (thief)), and an explicit understanding of ownership through their ability to attribute different property rights considering the legitimacy of the transfer. 3-year-old children did not make any distinction between the illegitimate and legitimate conditions in their evaluation, neither in their attribution of property rights. These results suggest that children acquire implicit and explicit understanding of ownership at the same time. In Study 1, no emotional reaction was present. We examined in Study 2 the role of the first possessor’s emotions in 3-year-olds’ evaluation of object acquisition. The same cue was present in the legitimate and illegitimate conditions: the first possessor being sad after both transfers. In the presence of this emotional cue, 3-year-olds managed to distinguish between the two conditions in their social/moral evaluation. This distinction could not have been based solely on the presence of a negative emotion, as the emotion displayed was the same in both conditions. We suggest that 3-year-old children detected the moral transgression in the theft condition, and used the negative emotion to confirm it. The studies in Chapter 3 (Studies 3 to 5) examined children’s evaluations of the restitution of an object to its owner. Young children (2-3-year-old) have a bias to consider that the first possessor of an object is its “owner” and that the object cannot be definitively transferred to someone else. We thus investigated whether 3-year-old children (Studies 3 and 4) implicitly evaluate the absence of restitution as a transgression, and evaluate it negatively compared to the restitution of an object to its first possessor…