The problem with collaboration is that there are temptations to defect. Explicit joint commitments are designed to mitigate some of the risks, but people also feel committed to others implicitly when they both know together that they each hold the other's fate in their hands. In the current study, pairs of 3-year-old and 5-year-old children (N = 192) played a collaborative game. One child was offered individual rewards (bribed) to opt out of the collaboration. In 3 different conditions, the level of the commitment was manipulated. Three-year-old children were more likely to resist the bribes when there was an explicit joint commitment to the partner than when they were only playing in parallel, with their reactions to an implicit commitment falling in between. Five-year-olds were more likely to resist bribes in both the implicit and explicit commitment conditions than in the no-commitment condition. Thus, children at both ages showed some level of commitment to a collaborative partner in the face of bribes to defect, but only 5-year-olds clearly appreciated that a common-ground understanding of interdependence between partners generates an implicit commitment or obligation.