I accidentally bought the first Trine instead of the sequel for me and 2 of my friends to play. We ended up playing and beating both in a weekend span. Those games are a lot of fun.
Steam is running a sale on selected coop games this weekend. Many of them are violent, like Serious Sam, so you'll want to stay away from those. But Castle Crashers is 75% off…
there is a free to play game on steam called unturned. its kind of a cartoony sandbox zombie survival game. it has guns and weapons but its done in a minecraft type of way and not over the top. you build bases and scavenge for food and water and equipment. the game is very fun two player. here is a video of the game. [video=youtube;NWIz8vKkJgQ]https://www.youtube.com/watch?v=NWIz8vKkJgQ[/video]