Yeah pokémon is too text heavy for a 6 yearl old unless he is a prodigy. He will be completely lost in the game.
It really depends on his personality though, but the sureway to go is with a 2DS and super mario (probably the 2D ones are better for an intriduction). It will help him develop his response time to stimulus.
If for example he is the quiet and calm type with developed speech, then you can try something a bit more complex like 3D world or even risk pokémon, cause he might be able to figure it out. Chances are thats not the case though. Actually, it would be safe to get him a 3DS if he was like this aswell.







