Actually your nervous system grows, the same way your body does. Your brain literally doesn't take its final form until around age twenty.
This was a major topic of conversation elsewhere, on a board devoted to Let The Right One In
a book/pair of movies/now two stage plays about a child vampire. Folks did a lot of research to show children literally do not think the way adults do, and has little to do with amount of experience. Not that experience doesn't have an impact of course.