Physical development during the first two years creates easily noticeable changes in appearance. While at birth the infant appears top heavy with his head approximately one-fourth the body length, by age 2 the length of the body has become more proportionate and is roughly half the adult height.
By age two the brain has developed to two-thirds of what it will weigh by adulthood and has increased to five times the density it was at birth.
What began as involuntary movement and reflexes at birth, by 6 months has become voluntary movements. By 2 years the fine motor skills are beginning to develop.
Although the least well developed at birth, with newborns focusing best on objects 4 to 30 inches away, by 6 months vision is nearing 20/20 and the ability to follow moving objects with both eyes has developed.
Hearing is comparatively acute at birth and newborns are able to distinguish their mother's voice from the voices of other women.