First, it is important to understand that children have to grow and develop in many different areas in order to become healthy, happy, productive members of adult society. There are four main areas or channels in which children grow: physical, psychological and cognitive, social and emotional, and sexuality and gender identity.
First, the physical channel is most obvious. Children's bodies grow in height and weight over the years and change appearance during puberty. Children also develop certain physical abilities during their progression towards adulthood, including crawling, walking, running and (possibly) writing or shooting a basketball.
Secondly, children also develop psychologically and cognitively as their brains absorb more information and they learn how to use that information. Literally, children have to learn how to think on purpose and to process or organize all the information that comes to them from the environment. They must learn how to solve problems, to talk, and to complete mental tasks such as remembering telephone numbers or using computers.
Thirdly, children grow socially and emotionally. They learn how to interact, play, work, and live with other people such as family, friends, teachers, and employers. They learn how to understand both their own feelings and others' emotions. They also learn ways of dealing with strong emotions. In order to function well as independent adults, children must develop a sense of self-esteem as they go through the long process of figuring out what shape their identity, or who they are, will take. They develop a sense of morality as they learn the difference between right and wrong.
Finally, children have to develop sexually and form a gender identity. This developmental channel is unique because it spans developments across the other physical, psychological, and social channels. Early on, children learn how their bodies work and look and what it means to be a boy or a girl; they learn how boys and girls are different. As they grow older and enter adolescence and puberty, they continue to learn how their bodies work sexually and how to responsibly handle their sexuality so as to balance their sexual desires and appropriate behavior. They continue to decide for themselves what it means to be masculine or feminine throughout their lifespan.