Human Growth and Development

Postnatal Development

Major Developmental Milestones During Infancy

A normal infant will double his or her birth weight by five or six months of age and triple his or her birth weight during the first year of life. Major developmental milestones during infancy are summarized in the table below. There is considerable variation between individuals, but these are within the normal range.

Age Major Milestones in Average Infant
End of first month Bring hands to face; move head from side to side while lying on stomach; hear very well and often recognize parents’ voices
End of third month Raise head and chest while lying on stomach; open and shut hands; brings hands to mouth; smile; recognize familiar objects and people
End of seventh month Roll over stomach to back and back to stomach; sit up; reach for objects with hand; support whole weight on legs when supported and held up; enjoy playing peek-a-boo; begin to babble
End of first year Sit up without assistance; get into the hands and knees position; crawl; walk while holding on; some babies are able to take a few steps without support; use the pincer grasp; use simple gestures—e.g., nodding head, waving bye-bye
End of second year Walk alone; begin to run; walk up and down stairs; pull a toy behind them; say single words (15–18 months); use simple phrases and two-word sentences (18–24 months); scribble with a crayon; build a tower with blocks


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