Developmental milestones include gross motor skills like sitting, walking, and balance, fine motor skills such as eating and writing, language skills such as speaking and communicating, cognitive thinking skills, and social skills including interacting with others. If developmental delays are not recognized early, it can be difficult for children to learn when they start school. In the United States, 17 percent of children have developmental or behavioral disabilities, but less than half are identified before starting school. The document provides additional resources on developmental delays.