While the importance of reciprocity has been shown in theoretical models and extensively studied in adults, little is known about the developmental trajectory of reciprocity in children. In the first part, I will provide a theoretical framework about the developmental trajectory of cooperative behaviors. In the second part, I will show a series of studies in which we adapted paradigms from adult research for studies with children, exploring when they begin to engage in tit-for-tat reciprocity, learn how to invest in a trust game, and bribe others.