At this age, mainly listen to great singers. Preferably those with light, pure voices, so he doesn't try to force immature vocal chords into creating mature sounds. Formal voice lessons are not really essential until puberty (unless you're contemplating the VBC, or something). (Hm. Listening to the VBC might be good, though.) Especially for boys, who will have to re-learn just about everything except for breath control at that point. Actually, learning diaphragmatic breathing would have value, even for a young child. It improves tone and control very quickly, for both singing and speaking. Also has handy beneficial side-effects for asthmatics.
