I started playing a simplified version of Warhammer Quest (mostly a simpler combat mechanism) with my 5 yo and 7 yo. We are still playing the game every now and then and they are 7 and 9 now. But a recent game I picked up was Zombicide. I have zero interest in zombies, my 7 yo son loves them and loves the game. “Best game ever” was one comment. He cannot sit down while playing and jumps up and down. It is a co-op games with figures with simple mechanics. I only have the first game but know there are lots of expansions. Games are 1 to 1.5 hours. I asked around and some other of my friends play it with their children too. I would have never thought of it but my son saw it second hand when we were wandering around.
Just my example and it may not be up your alley though!
WarhammerQuest is pure co-op play against the dungeon. You play a character (barbarian, dwarf, elf or wizard) and delve the dungeon fighting monsters and gaining treasure on the way to the final showdown. You do not need four – we usually play with three characters but you will need to tone down the number of monsters that appear.
I do have a post on my blog with the simpler combat rules and an example of play: