I think others have already hinted at what I'm going to say. Whatever you end up making, I would make it of a size that an adult could still comfortably shoot it. As any parent knows, they grow fast! A true "Childs rifle" would be outgrown quickly. Much better to make it slightly big and let them shoot it off a rest, that to have something that only fits them for about 3years, and is almost un-shootable as a teenager,.....which is normally when their interest level will begin rising drastically.