Hey, sourceforge.net recommend, among other few games, Simutrans for your hellish... uhu, I mean, your lovely kids to get them real busy these days:
https://sourceforge.net/blog/games-for-the-holidays/ (https://sourceforge.net/blog/games-for-the-holidays/)
BTW: Simutrans is thr 7th most popular game in the sourceforge.net.