A child in a dream can indicate you at that age. Commonly it will be one of your own children in the dream. A boy can indicate your male side or that you had issues with your father when you were the age of the boy in the dream. Likewise to dream of a girl can indicate your female side or that you had issues with your mother in childhood. We each have both male and female aspects to ourselves. Dreams always encourage you to restore balance to this energy mix. In fact that is one of the main purposes of your life.
If you dream of a number of children your age can be indicated by how many children there are. For example, seven children in the dream is about you at the age of 7.