This is the first I've checked this thread, and though I mostly agree with the replies you've been getting, I'd like to add a few thoughts.
Just make sure the sheath is secure enough to keep it from being lost, and strong enough that the blade can't puncture it during falls or be cut while drawing or resheathing. Think kydex. I recall falling and/or rolling around on the ground a lot more when I was younger.
I figure stainless steel would be better than regular hi carbon. I always used to hate the dark patina and rust that appeared on my blades.
Sharpening? I always seemed to have a lot more time to devote to this subject when I was little. By the 7th or 8 grade, my blades could easily cut free hanging hairs. (and also shave arm hair without touching the skin) There's simply no reason to assume a kid can't learn to sharpen properly; just give him some good instruction.
Many of my childhood knife memories were formed with a SAK type knife, but mine was a metal handled GI type folder made during WWII. I did carry it to school every day from the third grade until some lowlife SOB stole it in college. So, I can understand everyone's SAK recommendations. Man, I wish I still had that knife. When I got it, it was in mint condition, though it was already 40 or 50 years old- complete with blade etching.
That brings me to another point. Though there is a chance that he might lose or destroy it, there is still also a good chance he won't. Don't skimp on the quality. He will form a lot of memories involving this knife, and it will become a symbol of his growing maturity. I can't tell you how many times I've heard someone fondly reminisce about the cheap little .22 their dad gave them as a kid, but then when they get older they get themselves a "proper" rifle that was more accurate, more capacity, better quality, or whatever. They now realize that gun they idolized when younger is really nothing special. Wouldn't it be great if that first gun/knife was good enough to appreciate even as they got older?