I cannot recommend Trine 1 & 2 and Rayman Origins & Legends enough, they are perfect co-op choices to play with children. I played all of them with my daughter starting when she was about 6 years old. The Trine games are not difficult and encourage collaboration (and most difficult puzzles can be bypassed using the wizard’s levitation spells 
) and the Rayman games are simply delightful. Many difficult areas are optional and you can solo any difficult section (not too many, from what I can remember, though it’s been 3 years). **Pid **is also a good co-op choice, though we didn’t finish that one. Maybe starting it immediately after Rayman was a mistake, it did not possess the same charm.
We’ve also had many hours of great fun with Sonic & All Stars Racing Transformed. It’s colorful and joyful and my daughter even ended up posing a challenge for me after a while.
Before I forget: it’s important to use a gamepad for these games, at least for the kids.
You could also try some adventure games, there’s a ton of them and a good story will always appeal to kids. We played through Botanicula, Machinarium, Jolly Rover and Night of the Rabbit and started Broken Age. Next on the list are the **Samorost **games, **Lume **and Lumino City.
Other games we played, but may or may not be violent, depending on your point of view: Terraria (many many hours of building and exploration), **Towerfall **and, more recently, Duck Game. And we’re now in the middle of the coop campaign of Portal 2 (she’s almost 10 now, I’m not sure how a younger kid will manage).
