Each baby's rate of development is unique, with some babies able to smile or walk sooner or later than others. However, there are certain skill sets, known as developmental milestones, that all babies should be able to reach within specified age ranges. Developmental delays may be present if babies are consistently behind in acquiring certain skills or in babies who lose skills they once had. Although parents are usually the first to notice if their child seems to be behind other children of the same age, a diagnosis of developmental delay is usually made by a doctor following a strict set of guidelines, according to the University of Michigan Health System.
Muscle Control
Babies will gain control of different muscle groups as they develop, allowing them to perform such tasks as sitting and standing. By 3 months of age, babies should be able to hold up their heads and grasp objects. By 7 months of age, babies should bear weight on their legs, reach for objects with both hands, roll over, and sit with help. At 1 year of age, babies should be able to crawl, stand while supported, wave and point. By 2 years of age, babies should be able to walk and push a wheeled toy. According to the Centers for Disease Control and Prevention (CDC), failure to reach any of these milestones by their prescribed times could be the warning sign of a developmental delay.
Social Skills
Signs of delayed social development may be noticed as early as 3 months of age if a baby's response to new faces and surroundings causes alarm or of he is consistently inconsolable at night after 5 months. The CDC states that by 7 months, babies should appear to show enjoyment in the company of others as well as obvious affection for their caregivers.
Vision
Because babies lack the language skills to accurately convey their visual achievements there are few measurable milestones to track. According to the CDC, visual delays may be present if a baby's eyes are still crossed most of the time by age 3 months, if they can not follow objects with both eyes at both near and far ranges by 7 months, or if they do not point to objects or pictures by 1 year of age.
Hearing
Hearing delays can be observed early on in a baby's development. Babies should respond or startle to loud noises by 3 months of age and should orient or turn their head to locate the source of sounds by 4 months.
Language
Language skills develop at highly variable rates in babies. The CDC advises that concerns about language delays should be raised if babies do not begin to babble and imitate vocal sounds by 4 months of age or to smile by five months. Babies should also be able to squeal and laugh by 6 months of age and say their first words by age 1 year. To be considered within the range of normal language development, babies should have a vocabulary of at least 15 words and should be able to speak in two- to three-word sentences by age 2 years.
