Childhood is the age span ranging from birth to puberty. It may also include adolescence, but precedes adulthood regardless. According to Piaget's theory of cognitive development, childhood consists of two stages: preoperational stage and concrete operational stage. In developmental psychology, childhood is divided up into the developmental stages of early childhood (preschool age), middle childhood (school age), and adolescence (puberty to legal adulthood). Various childhood factors could affect a person's attitude formation.
The concept of childhood emerged during the 17th and 18th centuries, particularly through the educational theories of the philosopher John Locke and the growth of books for and about children. Previous to this point, children were often seen as incomplete versions of adults.