Interpersonal trust is a key component of cooperation, helping support the complexsocial networks found across societies. Trust typically involves two parties, one who "trusts" by taking on risk through investment in a second party, who can be "trustworthy" and produce mutual benefits. To date, the developmental literature has focused primarily on the trustor, meaning we know little about the ontogeny of trustworthiness. Whereas trusting can be motivated by self-interest, one-shot trustworthiness is more squarely situated in the prosocial domain, involving a direct tradeoff between self-interest and others' interests. However, this raises the question of whether trustworthiness is distinct from generosity. In this preregistered study, we examine the origins of trustworthiness using an intuitive version of the Trust Game, in which a first party invests resources in a second party who can split the gains. We recruited N = 118 5-to-8 year-old American children (M[subscript age]= 6.94, n = 59 girls, 57% White, 88% of parents with bachelor's degree or higher), split between the "Trustworthiness" condition, where another party's investment is instrumental for obtaining greater resources, and the "Generosity" condition, where the other party is a passive recipient. We found that children in the "Trustworthiness" condition shared significantly more resources than those in the "Generosity" condition. Further, children in the "Trustworthiness" condition predicted that the first party expected them to share a greater number of resources. Overall, these results demonstrate that trustworthiness is distinct from generosity in childhood and suggest that children spontaneously grasp and engage in a key aspect of cooperation.