I am not entirely sure on what account are you referring as "his account" ,but if it is a steam game maybe he can use your steam account or you can use the family sharing policy.Basically you can share a game from your steam library with another steam account and the only limitation is that you can't both play the game at the same time, but I don't think this will be a problem since you are buying it for your son.
If you mean you have bought it from "Windows Store" I think you can't share it with another ms account.
10-15-2015 01:32 PM