I'm looking for something new to play with my 7yo son. Mario games are a great amount of fun, but I'm feeling pretty burnt out and am looking to expand things a little bit. We are looking for cooperative games like Pikmin 3, Cuphead, and Hyrule Warriors rather than competitive-only games like Super Smash Brothers and Mario Kart. We appreciate whatever help you all can offer, so thanks in advance!
Ultimate Chicken Horse is easy and bloody fun. You have to get from point a to point b with your character multiple times and each time you either die or make it. Each turn you also place an obstacle each. Really fun. It's a favourite in our household.
Edit: sorry I didn't read your whole post. While it is competitive it's still fun... And different.
Stardew Valley!! The local co-op on the switch is my favorite way to play with my son. The game is so relaxing and once you get into it a bit it’s fun to see all of the ways we can divide up the chores and work together to make the farm better.
Sonic Mania has co-op! either you can take the lead as Sonic with your son as Tails, or vise versa! it's a great game, and a great introduction to the Sonic series
Untitled Goose Game actually has co-op in it. It's not a super long game, but it is a fun game. I played through the whole game with my daughter and she loved it. You can cause a lot of funny interactions throughout the game.
Unrailed is a cute, arcade-like, cooperative railroad track-builder.
Death Road to Canada is a hilarious parody of Oregon Trail set in the thick of a modern-day zombie apocalypse, and would help with his vocabulary-building. It's clean and has no profanity (and the zombies have black blood).