Longitudinal evidence for 4-year-olds' but not 2- and 3-year-olds' false belief-related action anticipation.

Recently, infants younger than 2 years have been shown to display correct expectations of the actions of an agent with a false belief. The developmental trajectory of these early-developing abilities and their robustness, however, remain a matter of debate. Here, we tested children longitudinally from 2 to 4 years of age with an established anticipatory looking false belief task, and found a significant developmental change between the ages of 3 and 4 years. Children anticipated correctly only by the age of 4 years, and performed at chance at the ages of 2 and 3 years. Moreover, we found correct anticipation only when the agent falsely believed an object to be in its last rather than a previous location. These findings point towards the fragility of early belief-related action anticipation before the age of 4 years, when children start passing traditional false belief tasks.