I would look at that package youth bow that Browning offers. Seems to be a great little bow for the money Around $170 to $220 depending on which one you get. They have two models to choose depending on the weight you son is able to pull. The cheaper one has a black riser and less weight and the mo0re expensive one has a camo riser and higher draw weight.
I too have to get my sone one here soon. I' ll most likley be purchasing this one later but for now he has a PSE that my uncle gave to him to use for now. He turns 11 in February and he has to wait until 12 to actually hunt big game here in Colorado. He does come along on an elk hunt every now and then though. He' ll be ready by 12. Heck he kept up with me at 11,000 feet this year.
Good luck with your son.