The developmental origins of sharing remain little understood. Using procedures adapted from research on prosocial behavior in chimpanzees, we presented 18- and 25-month-old children with a sharing task in which they could choose to deliver food to themselves only, or to both themselves and another person, thereby making it possible for them to share without personal sacrifice. The potential recipient, a friendly adult, was either silent about her needs and wants or made them explicit. Both younger and older toddlers chose randomly when the recipient was silent. However, when the recipient vocalized her desires 25-month-olds shared, whereas younger children did not. Thus, we demonstrate that children voluntarily share valued resources with others by the end of the second year of life, but that this depends on explicit communicative cues about another's need or desire. (Contains 3 figures.)