Step #1, In the Womb and Step #2, Infancy, are required reading before attempting to understand Childhood in step #3.
The entrance into childhood, unlike the entrance into Infancy, is a gradual transition. Childhood is recognized as the physical ability to speak and to walk and it is a condition of the person which lasts many years and moves through many stages. Our discussion is not concerned with the physical advancements but we will consider only the mental maturity of the person.
Unfortunately there are some who never advance to this stage in life. They remain completely self centered and self absorbed in spite of their physical advancement. However, for most individuals, childhood starts with a period of weaning. I do not refer to weaning from breast or bottle feeding, or both, but from being self centered. Most infants, are introduced to others of their age. They learn they have peers, people just like them. They also begin to understand language and concepts. At first meaning is conveyed to them through tone of voice and facial expression and after a time communication develops. They begin to walk. The ability to Walk and talk usually defines the transition to Childhood.
It is then, during the extended period of childhood, that a person is weaned from complete selfishness to maturity. It is a long and difficult period beginning with the sharing of toys and progressing, hopefully, to love and have compassion for others. Selfishness is deeply ingrained during the preceding periods even though the periods are short. But they are lifetimes to the emerging child.
The success attained during Childhood is dependent on the personality of the child but more, I think, on the guidance and example the child receives during that period. Example of parents and other adults has the most effect On them. They learn primarily by emulating what they observe. There are several stages of development in childhood but they all come together when we speak of mental (and spiritual) maturity. The child matures physically and he learns certain skills. The former is natural growth and the latter is a result of education. They can occur and in some cases do occur without mental maturity. A certain amount of sharing is forced upon them but unless, through the example of parents and other adults, they see and adopt selflessness and a sense of justice to some degree they may progress through childhood with little maturity. Religious training sometimes helps but unless they see that their parents put value in their faith, this too may fail.
There finally comes a time when they are given leave to drive a car and consume alcohol. They think that they are mature and their parents pat themselves on the back thinking the same. They go off into the world as adults. Many are functionally ready. Some are not. Some have not been completely weaned from selfishness. What makes it worse is that, for some driven by inflated egos and bad example, selfishness has been reinforced instead of being minimized.
They are left to mature in the next stage, Adulthood.