My first thought was Minecraft. I‘m not sure if it‘s playable offline still but a google search makes me believe so.

It runs on basically anything, and if the kids in question are still super young, there should be a peaceful/creative mode without monsters to scare them or survival mechanics to worry about, making it essentially just more complex LEGO.

Real. Without my 800 mods I would‘ve never bothered finishing it. Playing/modding was probably 50/50 in terms of time spent.

Horizon: Zero Dawn. I have yet to finish it but apart from robot dinosaurs, it feels so generically open world… Admitedly, a very pretty-looking open world. Can‘t really get into the story so far either since it takes itself so seriously while I‘m having a hard time not thinking too much about how ridiculous its world is. So apart from sight-seeing, there hasn‘t been much in this game for me thus far.

Edit: This comment section is a treasure trove of hot takes, so many of my beloved games mentioned making me go „What the fuck…,“ I love it