Babies grow quite rapidly during the first two years of life and can change in appearance and behavior from day to day. During these two years, a baby will grow and change quite significantly as he gains more complex motor skills and fine-tuned senses. The environmental, cultural and biological things that a baby is exposed to during this window of time all play a role in his growth, and the result of this collective group of influences is referred to as biosocial development.
Babies usually double their birth weight by 4 months of age and triple it by 1 year of age, according to Kathleen Stassen Berger, developmental psychologist and author of "The Developing Person Through Childhood and Adolescence." By their second birthday, children on average weigh 28 pounds, which is about one-fifth of their adult weight. They average 34 inches in height, which is about half of their adult height. Getting proper sleep during these two years is crucial for normal development, and not getting enough sleep is correlated with physical development delays, Berger says. Proper nutrition is also vital.
Brain development is the most important part of biosocial development, notes Russell Isabella, a professor and chairperson of the Department of Family and Consumer Studies at University of Utah College of Social and Behavioral Science. A baby's head circumference will increase during the first two years, and this indicates that his brain is growing and developing. By age 2, the brain is about 75 percent of the size it will be in adulthood, Berger notes. The dendrites, axons and synapses of the brain increase in number, as well, allowing the baby to gain new skills such as walking and talking. Giving babies ample time to sleep, play and interact with parents is necessary for brain development. Good nutrition is essential, too.
Five Senses Development
In combination with brain development, during the first two years a baby will gain various skills related to the five senses. Though babies are born with the ability to see, hear, smell, taste and touch, they gain the cognitive ability to make sense of stimuli during the first two years. Babies develop binocular vision around 14 weeks of age and hone their ability to focus. They develop depth perception by around 6 months of age. Parents who talk to, smile at and touch their babies can help encourage normal development of the five senses.
Motor Skills and Movement Development
As babies grow, they gain gross and fine motor skills that allow them to become mobile. For example, by about 6 months of age a baby will be able to reach for and grasp an object, a fine motor skill, and by 8 to 10 months of age a baby is able to crawl, which is a gross motor skill. Other gross motor skills learned during the first two years of life include holding up the head, rolling over, sitting up, pulling to a standing position, cruising along furniture, walking, running and kicking a ball. Fine motor skills that babies gain during the first two years also include picking up bits of food, feeding themselves with a spoon and learning to scribble with a crayon.