My 8yo twins enjoy Mysterium, they can make it through most of a round of the new Dark Tower (with help of course), and they are just starting to learn and enjoy Castle Panic. I think within a year or so they'll be able to do Pandemic, and shortly thereafter we'll introduce Ghost Stories and Defenders of the Realm.

All of these are great coop games for adults too, among my favorites. I recommend the expansions for Castle Panic.

The Forbidden series is good too, probably even more suitable for the younger set than these.