On the switch Luigi's Mansion 3 is great. Got close to 10 hours of play working on the main story with my 5 year old playing as gooigi. With everything unlocked my 5 year old and 3 year old have fun roaming around the hotel catching ghosts. Plus there's some fun mini games.

Lovers in a Dangerous Spacetime.

Overcooked.

Overcooked 2

Up to 4 player Co-op. Incredibly fun games.

Source: I play co-op and versus games with my kids. We've incorporated casual video game play into our family time for the past few years.

Mame has lots of great multiplayer games. As an example, we've been playing Trog and Gain Ground lately as a family.

Bubble Bobble is another obvious choice, but really there are thousands of 2-4 player coop games.

You can usually set the difficulty directly in the arcade machine setup, or by proxy by limiting yourselves to a certain number of coins.

A warning that unlimited coins can just make a game a never-ending grind because you don't have that failure/reflection loop to skill up between attempts and you can end up way beyond your ability to succeed by just feeding coins in.

I picked up Unravel 2 and have been playing it with my non-gamer girlfriend - she's had no problem picking it up and it's quite fun and challenging for both of us, both from a technical perspective (Most puzzles only require precise inputs from one player) and a mind-twister perspective. I believe it is only two player co-op, though, so if you've got more than one kid to entertain then this one might not be for you.

The Lego games can be really good with younger kids.

FIFA / NBA 2K for older kids.

Smash brothers, Luigi's Mansion, Marvel games on ps4, Lego _____ games.

Castle Crashers, Children of Morta. A little more violent, things like risk of rain, chaosbane, diablo 3, inquisitor martyr.

Check out this site too: https://www.co-optimus.com

This is what we need VR games for - to bring back co-op with the kids!