Chill man, no worries. He can own a long gun just like you can as long as he isn't a felon and has not committed a violent misdomenor.
I quote:
"(B15) May a parent or guardian purchase firearms or ammunition as a gift for a juvenile (less than 18 years of age)? [Back]
Yes. However, possession of handguns by juveniles (less than 18 years of age) is generally unlawful. Juveniles may only receive and possess handguns with the written permission of a parent or guardian for limited purposes, e. g., employment, ranching, farming, target practice or hunting. [18 U. S. C. 922( x)] "
http://www.atf.gov/firearms/faq/faq2.htm#b15
So let us say your kid is walking through the woods on your property with his SKS. He can, LEGALLY, say that he has it for protection against dogs. Nobody can arrest either of you as the possession was lawful and since handguns are specifically excluded (although a letter can change that) nobody can say his choice was poor. Or, he could also be hunting, assuming it is legal to hunt in that area with rifles and he is 50 feet from a road, 300 feet from someone elses house, etc. No liscense is needed to hunt on property owned by immediate family (brother, sister, mother, father, son, daughter).
The above is VA, so take note of that. I saw you were in VA so figured I would let you in on that piece of information. Technically as long as he is on your own property (if you can shoot there) he can also shoot it by himself. It was lawfully purchased for him and it is NOT reckless endangerment; he knew how to use it and it was specifically purchased for him, he didn't "find it" by accident.
If you follow the above, make sure he is 100% safe though. No unlawful firearms possesion, but if he handles it wrong that is wreckless handling of a firearm.
The law sucks, but read it closely, we generally have more freedoms than we care to accept or notice.