If your son isn't going to use it for online games when out and about, then you don't need the 3G option....at home he can connect via wifi.
It has a slot for a memory card so you'll need one of those for him to be able to save games etc.
Whether you get one with games really depends if he likes the games on offer. Otherwise you can buy new or pre-owned games in stores like Game.
My husband likes his but I prefer my PSP