What game should I get [360]?

I have only a 360 for split screen multiplayer and I want to play with my 12 y/o cousin. What game should I get? It should have low violence, for he does not like violent games, or in fact fantasy, party, or racing games either. It would also be nice if it had a sci fi theme.

Portal 2, offline split screen Co-op is possible.

portal 2

Portal 2.

Portal 2

Portal 2, is a brilliant fantastic game. Sadly there isn't very many co-op games. There is a game called Hunted the demons forge but I believe it might be rated M

Splosion Man and Ms Splosion..... Its better than mother's milk.

There is a game called fusion frenzy 2

The first one was great when I was a kid.

Never played the 2nd one, but I imagine it's great too.

Portal 2