First off, check out the Civilian Marksmanship Program for location of a CMP club near you. Many offer youth marksmanship training. Click on the following link:
Civilian Marksmanship Program
Select "Club Info", then "Affiliated Clubs"
Many of these clubs have rifles available for use by youngsters and you can try them out to see what works best for him. Most have certified instructors that will be glad to offer help/suggestions.
You might click on "Sales" and then "Rifle Sales" to see what CMP has to offer in way of rifles. They Used to have various smallbore rifles relatively cheap, but not sure what they currently offer. Our club had some CMP Mossberg 144's but found them to be too heavy for the smaller youngsters.
Definitely teach him to shoot right handed. My wife is nearly blind in her left eye, but is left handed. I taught her to shoot right handed very easily since she had never learned to shoot left handed. Much tougher to switch later on.
Agree w/previous posts suggesting a "full size" rifle as opposed to the chipmunks. Stocks can be cut to fit and either replaced later or put back together. If you plan to cut the stock and add the cut piece back when he grows into it, remove the butt plate and drill two 1/4" holes past the point you plan to cut off. This makes it simple to align the two pieces by driving 1/4" dowel coated w/glue in holes, then all you have to do is sand stock and refinish when piece glued back on.
Take the boy out and get him started! You'll both have a ball.
Regards,
hps