During Piaget's sensorimotor stage
(birth to age 2), infants and toddlers learn by doing: looking, hearing, touching, grasping, sucking. The process appears to begin with primitive “thinking” that involves coordinating movements of the body with incoming sensory data. As infants intentionally attempt to interact with the environment, they learn that certain actions lead to specific consequences. This is the beginning of the infants' understanding of cause‐and‐effect relationships.
Piaget referred to the cognitive development occurring between ages 2 and 7 as the preoperational stage. In this stage, children increase their use of language and other symbols, imitation of adult behaviors, and play. Young children develop a fascination with words—both “good” and “bad.” They also play “pretend” games. Piaget also described this stage in terms of what children cannot do. He used the term operational to refer to reversible abilities that children had not yet developed. By reversible, Piaget meant actions that children perform in their mind, but that can occur in either direction. Adding (3 + 3 = 6) and subtracting (6 − 3 = 3) are examples of reversible actions.
Piaget believed that egocentrism—the inability to distinguish between one's own point of view and those of others—limits preschoolers' cognitive abilities. The capacity for egocentricity exists at all stages of cognitive development, but becomes particularly apparent during the preschool years. Young children eventually overcome this early form of egocentrism when they learn that others have different views, feelings, and desires. Then they can interpret other's motives, and use those interpretations to communicate mutually—and therefore more effectively—with others. Preschoolers eventually learn to adjust their vocal pitch, tone, and speed to match those of the listener. Because mutual communication requires effort and preschoolers are still egocentric, they may lapse into egocentric speech (non‐mutual) during times of frustration. That is, children may regress to earlier behavioral patterns when their cognitive resources become stressed and overwhelmed.
Piaget also believed that young children cannot grasp the concept of conservation, which is the concept that physical properties remain constant even as appearance and form changes. They have trouble understanding that the same amount of liquid poured into containers of different shapes remains the same. A preoperational child will tell you that a short, fat bottle does not contain the same amount of liquid as a tall skinny one. Similarly, a preoperational child will tell you that a handful of pennies is more money than a single five‐dollar bill. When children develop the cognitive capacity to conserve at around age 7, according to Piaget they move into the next stage of development, concrete operations.