I had a 7-year old girl who wanted a harmonica as a gift. I couldn't find one with big holes (although I think someone on this list mentioned a harp like that a whiles back). I did the next best thing and bought something cheap. I bought one of the Hohner knockoffs built in China called the "Bluesband" which was only five bucks. This harp is an imitation of the Bluesharp, before it went modular. Anyway, she seemed to be able to play it just fine (for a 7-year old).
By the by, I was listening to the Essential Little Walter yesterday, and does anyone disagree that "Mellow Down Easy" is a rockin' tune?!?!?! The lyrics are fun and Walter honks a hard, but controlled harp throughout, particularly in the middle of the tune (right when, one of the background musicians shouts some encouragement at him). Is this tune in the key of G, harp key C?