Humans routinely share valuable resources, even at significant personal cost (e.g., organ donation). What motivates such generosity? This study examined the emotional benefits of sharing in toddlers with the largest and youngest sample to date (N = 134; Mage = 20.50 months, range = 16.57-23.77 months). Replicating prior studies, toddlers displayed greater happiness after giving than receiving. Extending these findings, we demonstrate that sharing resources provided by an experimenter elicited greater happiness than observing the experimenter share, suggesting that actively performing prosocial acts leads to greater reward. Crucially, we ruled out alternative explanations by demonstrating that the emotional benefits of sharing are not attributable in this study to emotional contagion (toddlers' happiness was unrelated to recipient's enthusiasm) or following an experimenter's instructions (toddlers were happier giving to others than to themselves). These findings provide evidence that sharing is intrinsically rewarding from shortly after it first emerges, which may serve as a proximate mechanism driving cooperation across societies. SUMMARY: We provide evidence that sharing is intrinsically rewarding soon after this behavior emerges in ontogeny. Toddlers displayed greater happiness after giving than receiving, and actively sharing resources led to more happiness than merely observing sharing. Giving to others elicited more happiness than giving to oneself, suggesting that sharing is emotionally rewarding due to its prosocial nature.