As someone who has spent about 4 months total of my life living out of a hammock in a desolate s@#$-hole, I think the first thing you should do, is get a basic parachute nylon style hammock. They are lightweight, modular, and easy to use. I am of slightly above average height and find the ENO doublenest to be perfect for my needs.
For a child, I would buy this and see how they like it
http://store.grandtrunkgoods.com/ultralight-travel-hammock1
Its cheap, light, and easily packed, and it doesnt come with carbiners, so you can find th exact right setup carbiners for your son. Despite the low cost, the Grandtrunk travel hammock is a real tough piece of equipment, I have had one up in the front yard of a place in virginia for over a year now, year round, wind/rain/snow etc.
If the kid loses or tears it u, well then it was just 20 dollars wasted, but if he likes it, and wants to keep going with it, you can upgrade to an ENO, hennesey, jungle hammock or warbonnet and keep the grandtrunk as a reserve for friends or torn hammocks.
If i were you, i would mosey on down to hammock forums nd lurk a bit, the people there are awful friendly if a bit goofy.
Good luck.