Any delay in a child's physical, cognitive, behavioral, emotional, or social development, due to any number of reasons.

Developmental delay refers to any significant retardation in a child's physical, cognitive, behavioral, emotional, or social development. The two most frequent reasons for classing a child as having developmental delay involve those psychological systems for which there are good norms. This is especially true for motor development and language development. Because it is known that all children begin to crawl by eight months of age and walk by the middle of the second year, any child who was more than five or six months delayed in attaining those two milestones would probably be classified as developmentally delayed and the parents should consult the pediatrician.

Most children begin to speak...