Linux Gaming

Since you mention Baldur's Gate 3 you could try Divinity Original Sin and DOS2, DOS has 2 player coop by default and with mods you can play 4 player, DOS2 has 4 player coop out of the box.

Although depending on how old your kids are it might be difficult to play.

Someone else already mentioned the lego games and I can't 100% recommend those as well. Lego Star Wars complete saga, lego star wars clone wars, lego indiana jones are the ones I've played and can recommend all of them.

Although there's only 2 player coop.

Some of the best family friendly co-op games I've played:
Stardew Valley
Valheim
Don't Starve Together

There are a ton of couch co-op games! Just not AAA

• Ultimate chicken horse (great for kids!)
• It takes Two
• Overcooked 1 & 2 (difficult for kids)
• jackbox games for parties
• Super Bunny man
• cuphead
• human fall flat
• lovers in a dangerous spacetime
• magika
• all Lego games (they have everything for kids interests)
• moving out 2

You didn't mention ages, but my kids liked the LEGO games. We played through Harry Potter, LEGO City Undercover, Marvel Superheroes, and Jurassic World, and there are a few more we haven't played yet. They'll run on a potato and they're really fun.

They aren't RPGs though, but for my kids, that didn't matter. They could role play just fine with the characters they could pick between.

Other than that, there are some others that may fit the bill, but they often have mature themes, like Divinity Original Sin and Wasteland, but hopefully those give you enough to find something that'll work.

I personally play a lot of single player games with my kids watching. We're playing through Zelda games right now, but we've played a number of games on PC as well. I'll sometimes let them control things for a bit if they want, but generally I'm the one actually playing.

Not sure how old your kids are, but mine are 7 and 11 and I would definitely NOT play BG3 with them. If it were a movie, I don't think it would even get an R rating given all the sex and gore.

(To be clear, not judging the game. I quite enjoy it. Just don't find it appropriate for my little ones. Caveat emptor.)

FWIW, I had a lot of fun playing thru Portal with my son. No official co-op mode in the first one, but the second one has it and it's pretty old at this point so should run fine on older machines.

You can open a project in C++ to create the structure of a custom game. You put one child to work on blender or pixelart software, and another child to compile variables and functions. If you have more than two children, you can also consider assigning a third to animation and a fourth to creating music and sounds.