Three- and four-year-old children represent mutually exclusive possible identities.

How do children think about and plan for possible outcomes of events that could happen in the future? Previous work that has investigated children's ability to think about mutually exclusive possibilities has largely focused on children's reasoning about one type of possibility-the possible locations of an object. Here, we investigated children's reasoning about another type of possibility-mutually exclusive possible identities. In two experiments (N = 201 U.S. 3- and 4-year-olds), children were told that two animal characters (e.g., a bunny and a monkey) were going to take turns sliding down a playground slide. Children were told that the animals wanted to eat their favorite foods (e.g., carrots and bananas, respectively) as soon as they got to the bottom of the slide. In an Unambiguous Identity condition, we told children the identity of the animal that would slide down. In an Ambiguous Identity condition, we told children that which animal would slide down first was unknown. To examine children's representations of possible identities, we asked children to "get snack ready." We found that children in the Unambiguous Identity condition selected only one of the snacks (i.e., the favorite snack of the animal they were told would slide down), whereas children in the Ambiguous Identity condition selected both snacks, suggesting that they were accounting for both possible identities. These results extend the literature on the development of modal reasoning to include reasoning about possible identities and suggest that this ability may be available to children as young as 3 years.