Kanck on PS4 was purpose built for this sort of thing. The game's coop has the second player control a robot Knack to help the first player in combat that infinitely respawns whilst the first play is Knack and controls the game like a single player game.
My son wan Five at the time we played through it together and I'd say that age and up to about 3 years older is about the correct age for this to work as intended. I point that out because I don't know how old your son is, so might not be the right age for this.
EDIT: It appears he's been banned. Oh, well...