In three experiments involving 207 preschoolers and 28 adults, we investigated the extent to which young children base moral judgments of actions aimed to protect others on utilitarian principles. When asked to judge the rightness of intervening to hurt one person in order to save five others, the large majority of children aged 3 to 5 years advocated intervention in contrast to another situation with the reverse cost/benefit ratio. This course of action was seen as acceptable by most children only when it did not require the agent to have physical contact with the victim and the victim's harm was intended to produce the greatest good for the greatest number. Overall, the children's responses were remarkably similar to those reported in adult studies. These findings document the extent to which some constraints on moral judgment are present in early human development.