If I had a little kid (and boy am I glad I never did) and I wanted to break him in to ML shooting, I would build him a .32 or .36 half-stock percussion gun with a stock sized to fit him or a skinch longer. Then when he got older I would make another stock to fit him and have him help build it to boot. Kids take better care of stuff if they have a hand in building, not to mention a lessened chance of him selling it for beer money when he's in college.