Sarah, people grow up, even children. One time they are children and like to play. Five years later they say things like "Dad, you're not actually rich", or they ask mature questions. On a movie on Saturday a teenage girl asked her father, why he and her mother don't live together any more (well, not much), and John Wayne told her that that was an issue between the parents, he and his wife.
In your confusing story above, (hard to work out who is who?) the boy Andrew is evolving into 'someone entirely new'.
The child is growing up and maturing. He is becoming his own person, and not a dependent of his parents. It is like in some songs, where they sing words like 'becoming whom I am meant to be' or 'becoming who I really am'. This child Andrew is growing out of childhood and becoming himself, a completely new person to who he was as a young child. He is becoming adult, and not an appendage of his parents.