* childhood, and
Each stage is characterized by a general cognitive structure that affects all of the child's thinking (a structuralist view influenced by philosopher Immanuel Kant). Each stage represents the child's understanding of reality during that period, and each but the last is an inadequate approximation of reality. Development from one stage to the next is thus caused by the accumulation of errors in the child's understanding of the environment; this accumulation eventually causes such a degree of cognitive disequilibrium that thought structures require reorganizing.
The four development stages are described in Piaget's theory as:
from birth to age 2. Children experience the world through movement and senses (use five senses to explore the world). During the sensorimotor stage children are extremely egocentric, meaning they cannot perceive the world from others viewpoints and explore using senses.
The sensorimotor stage is divided into six substages: "(1) simple reflexes; (2) first habits and primary circular reactions; (3) secondary circular reactions; (4) coordination of secondary circular reactions; (5) tertiary circular reactions, novelty, and curiosity; and (6) internalization of schemes."  Simple reflexes is from birth to 1 month old. At this time infants use reflexes such as rooting and sucking. First habits and primary circular reactions is from 1 month to 4 months old. During this time infants learn to coordinate sensation and two types of scheme (habit and circular reactions). A primary circular reaction is when the infant tries to reproduce an event that happened by accident (ex: sucking thumb). The third stage, secondary circular reactions, occurs when the infant is 4 to 8 months old. At this time they become aware of things beyond their own body; they are more object oriented. At this time they might accidentally shake a rattle and continue to do it for sake of satisfaction. Coordination of secondary circular reactions is from 8 months to 12 months old. During this stage they can do things intentionally. They can now combine and recombine schemes and try to reach a goal (ex: use a stick to reach something). They also understand object permanence during this stage. That is, they understand that objects continue to exist even when they can't see them. The fifth stage occurs from 12 months old to 18 months old. During this stage infants explore new possibilities of objects; they try different things to get different results. During the last stage they are 18 to 24 months old. During this stage they shift to symbolic thinking.
from ages 2 to 5 (magical thinking predominates. Acquisition of motor skills) Egocentricism begins strongly and then weakens. Children cannot conserve or use logical thinking.
Concrete operational stage:
from ages 5 to 11 (children begin to think logically but are very concrete in their thinking) Children can now conserve and think logically but only with practical aids. They are no longer egocentric.
Formal operational stage:
after age 11 (development of abstract reasoning). Children develop abstract thought and can easily conserve and think logically in their mind.