Should I get my son minecraft for xbox?

Yes, minecraft is actually very educational and will bring out your sons creative side. There's not much violence that goes on and no blood and gore whatsoever

I think he is a little small, you could give some math game

I suggest you get a game engine/3d modeling program instead.
There are plenty of free to download ones online. With that there's no limit to what you can create and learn.
I disagree when people say MineCraft is "educational".

Yes, it lets a kid be creative but don't let him get addicted

IT IMPROVES A CHILDS IMAGINATION SKILLS. So HE MUST PLAY THAT GAME