I recommend Astroneer - a solo / multiplayer survival game about collecting resources, refining stuff and building up bases on several planets. It’s hecking fun in multiplayer and it doesn’t have combat. There’s a ton of things to do and if the kids are good at communicating with each other they can quickly conquer the game. The only microtransactiony stuff it has is cosmetics (but it’s not being pushed upon you in any way), but you can unlock some of these through progression as well.