Try the Mathews Genesis or Mini Genesis, it's a great little bow for the money and your son can grow into it as there is no specific draw length. It has a short axle to axle length and is only 2lbs in total weight. Draw weight is 6-12lbs adjustable and depends on how far you draw for the weight. I wouldn't waste my money with the 'Lil Braves or Golden Eagle youth bows. I have 2 boys and have been there....they make junk and it'll break in no time, believe me Mathews is way ahead of everyone in this dept.
http://mathewsinc.com/mathews-bows-MiniGenesis-44-ViewProduct-1375-287.asp I bought my Genesis Pro from here :
http://www.genesis-outlet.com/order.html You can buy the kit that comes with the bow, arrows, a quiver, and an arm guard
I love shooting this bow for just fun and Genesis Outlet has extra arrows and accessories. They also have great customer service.
I believe you can get it from Cabelas and Bass Pro as well.
Another great little bow for little guys is the Hoyt Banshee. I bought one for my 6yr old last (7yrs old now and still uses it) year. I tried to talk him into the Mini Genesis but he had to have one like his dad, I bought the Hoyt Trykon that I hunt with. I'm not sure if Hoyt makes the Banshee still as they change every year but I know Mathews still makes the Genesis (Mini Genesis, Genesis, and Genesis Pro) and in my honest opinion cannot be beat by anyone in the same business. As far as the money part, like I said he can grow into these bows and use the mini for many more years, the genesis throughout his adulthood. So i'd say its worth the extra money
If he plans to hunt, most states require at least a 40lb pull, then check out the Hoyt Trykon Jr. Personally speaking, I myself would not buy anything other than a Hoyt or a Mathews. I have owned, target shot, and hunted with both brands for years and the others out there just don't compare.