I would take him and the bow to a proshop. Most will be happy to adjust the bow and cut arrows for you. Not that it really matters much at this point, but I like the idea of getting a youngster started working with someone at a pro shop. They begin to recognize that bowhunting is different than any other kind of hunting. The begin to see the complexity and thought that goes in to shooting a bow. It is a great outing for uncle/nephew as well.
Thanks,
Jack