Children gain new insights into how other minds work sometime between ages 4 and 5. Part of this understanding includes realizing that people can believe incorrect things about the world. In one experiment, children are shown a closed tube with images of candies on it and asked to say what is in the tube. Children usually say “sweets” or candies, but when the tube is opened, they see that there are pencils inside. Then the tube is closed again, and children are asked to describe what one of their friends will think is inside the tube when they see it for the first time. If they understand that people can perceive something incorrectly, they will answer “candies” even though they know that there are pencils inside. Before around age 4, children answer “pencils,” showing that they don’t yet understand how people can believe something that is false. After age 4, most children answer correctly.
Perner, J., Leekam, S. R., & Wimmer, H. (1987). Three-year-olds’ difficulty with false belief: The case for a conceptual deficit. British Journal of Developmental Psychology, 5, 125