• People have mentioned it yet, but I want to second It Takes Two, such a fantastic game! Story might not not appeal to everyone, because of relationship drama and a particular scene, but younger kids tend to ignore it and gameplay is a blast anyways! (Platinum’ed it with my then 8yo son.)
• Death Squared is a great cooperative puzzle game for 1, 2 or 4 players.
• The Overcooked! games are really nice coop games, albeit more and more chaotic the further you move on.
• Moving out is similar to Overcooked, but haven’t played it myself.
• ibb & obb is such a cool lo-fi coop platformer.
• Shift Happens is another cool coop platformer, and costs almost nothing.
• Unravel 2 is another gem in coop platformers, with quite a moving story.
• Pikuniku is very cool for younger kids, and a very funny game, too!
• Minecraft Dungeons is a nice Diablo clone, but not that dark and suitable for younger players.
• You can’t go wrong with Tetris. I personally like the Puyo Puyo Tetris variants and Tetris Effect.