The age at which a child begins to be able to do certain key kinds of activities, especially in the area of motor skills, cognitive skills, self-help skills, social skills, and communication skills. A Chart of Normal Development, reproduced, indicates when, between birth and age six, children first on the average begin to do certain things. Note (as the materials accompanying the chart explain) that children may vary widely from the average as to when they reach certain milestones and still be quite normal. But if a child is seriously delayed (called developmental delay) in one or more skills areas, parents may want to consult their pediatrician to see if there is a problem, especially one that might benefit from early diagnosis and treatment.
A skill regarded as having special importance in the development of infants, toddlers, and older children and teens, usually associated with a particular age range (e.g., sitting, crawling, walking, language acquisition).