I think I have to agree with Dean's rattan kid's bow design.
I would, however, (personal preference), not teach him to pinch the nock. I teach three fingers under, and -always- use a properly sized serving for the nock and good nockset. It has been my experience that kids that are capable of making the Boy Scout salute with their hands are ready to shoot. Otherwise they need to grow a bit. I have taught this to kids from 2.5 years old to 82 years old.
I also use a 1/2" PVC tube, 4" long, with an animal balloon passed through it and ends tied together to teach proper form and release, -before- I put a real bow into the kid's hands.
I have to finish up my new kid style quiver to post for you. I think you'll like it. Check next week.