[Aliantha]

This is from wiki and is a fairly good explanation of Piagets theory of cognitive development. Note that Piaget talks about environment and events shaping the way children evolve as opposed to inate stages of development which is a theory prefered by other equally respected child psychologists.

Although there is no general theory of cognitive development, one of the most historically influential theories was developed by Jean Piaget, a Swiss psychologist (1896–1980). His theory provided many central concepts in the field of developmental psychology and concerned the growth of intelligence, which for Piaget, meant the ability to more accurately represent the world and perform logical operations on representations of concepts grounded in the world. The theory concerns the emergence and acquisition of schemata—schemes of how one perceives the world—in "developmental stages", times when children are acquiring new ways of mentally representing information. The theory is considered "constructivist", meaning that, unlike nativist theories (which describe cognitive development as the unfolding of innate knowledge and abilities) or empiricist theories (which describe cognitive development as the gradual acquisition of knowledge through experience), it asserts that we construct our cognitive abilities through self-motivated action in the world. For his development of the theory, Piaget was awarded the Erasmus Prize. Piaget divided schemes that children use to understand the world through four main stages, roughly correlated with and becoming increasingly sophisticated with age:

Sensorimotor stage (years 0–2)
Preoperational stage (years 2–7)
Concrete operational stage (years 7–11)
Formal operational stage (years 11–adulthood)