At the beginning of the preoperational stage, children have mastered the skill Piaget termed the semiotic function -- the ability to mentally represent objects and people. Children begin to master symbolism during the preoperational stage, which might be why children at this age are so fascinated by make-believe play. A broom quickly becomes a car and a dog can easily be a horse. While logical thinking is not yet fully developed, preschool children develop rudimentary reasoning skills and become much more curious, frequently asking "Why?"
Children in the properational stage of development are highly egocentric. Their conversations and thoughts tend to center around themselves, and they often attribute their own feelings to someone else. While preschool children at this age are beginning to develop empathy, they still struggle to understand how someone could feel differently than they do. A 3-year-old, for example, might insist that her mother likes ice cream -- despite her mother's protestations -- because the child likes ice cream. Children at this age struggle to take another person's perspective. For example, a child who is shown where an object is hidden while another child is out of the room will mistakenly believe that the other child knows where the object is hidden.
Children at the preoperational stage struggle with the concept of conversion -- the fact that an object can change shape but still be the same. For example, a preschooler who saw a small amount of water in a small glass and then saw the same amount of water in a larger glass might believe that the glasses contained different quantities of water. Preschoolers can't yet think using formal logic and can only understand simple consequences. Moral realism -- the belief that everyone else holds the same values as the child -- is also a hallmark of the preoperational stage.
Many psychologists have contested Piaget's stage theory. Lev Vygotsky, for example, argued that development is partially a product of culture and that children enter developmental stages because of informal training, not as part of an innate developmental trajectory, according to Robin Harwood in the textbook "Child Psychology." In her book, "The Cultural Nature of Human Development," Barbara Rogoff emphasizes that children hit developmental stages at different times depending upon the culture in which they are raised and that the standards of the preoperational stage might not apply in every culture.