Infancy is a time of intense development. Babies start out with little more than instinctual reflexes and an innate ability to learn. Over the course of two years, they progress to the point where they have recognizable personalities; are able to move themselves from place to place and manipulate things; and understand how certain important aspects of the world operate (such as object permanence; the understanding that objects continue to exist even when you are not looking at them). They understand the rudiments of how to make their wishes known, have formed attachments and relationships, and have learned basic ways of managing their emotions and impulses. While these achievements are tremendous and set the stage for later learning, they are also commonplace. So long as children are born without significant illness, and so long as they are properly nurtured and cared for, their development towards these achievements will likely progress uneventfully.
The key phrase is, of course, "properly nurtured." As Bronfenbrenner stressed, child development is influenced by the environment at every level. Children progress toward milestones through interaction with their physical environments, with loving parents, and with the larger world. Problematic or lack of nurturing has a negative impact on their ability to progress smoothly. Children who are not exposed to language and communication stimulation, either because of hearing problems or caregivers' neglect to speak with and around them, can have difficulty learning more complex language skills in later years. Similarly, children who are deprived of consistent nurturing care can grow to learn to mistrust others and have problems bonding with caregivers or other people in later years. Good parenting skills can help smooth out some of the inevitable bumps and bruises that might threaten to derail more sensitive or temperamental children. Though all parents will make mistakes in the 22 years it takes to raise a child; love, attention, and care provide strong bedrock for healthy child development.
Development doesn't stop here, of course. When it is ready, the next document in this series will discuss how children progresses into the next stage of development, the preoperational stage, which lasts from ages 2 through 7.
Babies grow at an amazing rate in the first months and years of life as they rapidly reproduce cells and grow in length and weight. In the first 2 years, babies grow to almost half their adult height and can quadruple their birth weight. During this period, it's important for caregivers to take their infants to the pediatrician for well-baby checkups (during which they will be weighed and measured) on a regular schedule to make sure they are growing at the appropriate rate. During the first year, babies will continue to increase their level of body fat. This "baby fat" allows a baby to maintain their body temperature. As babies grow in size and begin to build muscle, this baby fat will begin to disappear.
In the first two years of life, a growing child's bodily proportions also change. When infants are born, most of their body mass is in their head. As they grow older, the rest of their bodies catch up. Just as they develop their motor skills from the center of the body outward and from their head to their feet, they also grow and gain mass in that order. Babies grow first in their chest and trunk and then in their arms and legs. Over the first year of life, babies' bones and skeletons ossify, or harden. When babies are born, their bones are softer and more like cartilage. This allows them to be flexible, fit inside the mother's womb, and pass through the birth canal. However, as their bones harden in the first year, the skeleton is better able to support their weight during activities such as crawling and walking. Babies also have "soft spots" in their skull because some parts of the skull haven't fused together yet. By age 2 years, babies' skulls are as hard as adult skulls, but in the first months, caregivers need to be careful how they handle the baby and protect their heads.
As noted before, infants grow exponentially in the first 2 years. In the first 3 months, they grow up to 2.5 inches and 3 pounds. Between the ages 4 to 6 months, they grow another 2.5 inches and gain an average of 4 pounds. Between 7 and 9 months, they grow an average of 2.5 inches and 4 pounds. Between 10 and 12 months, they grow another 2.5 inches and another 3 pounds. During the second year, toddlers grow about 1 inch and 2 pounds about every 3 months. Children's growth slows considerably after age 2 years.