If you want a more kid friendly FPS, go with Portal 2. My son and I play it a bunch. You can do it split screen, but many times he'll jump on the upstairs PS3 and I'll be on the one in my bedroom.
He's also a big fan of the Ratchet and Clank games. All 4 One has MP Co Op.
Pinball is fun, but the MP is kinda lame. You don't get to watch the other player play, it's more of a race to see who can reach a goal first. I know there'd be some downtime with it, but I'd like the option to watch the other player's turn.