I have a few kids, and setup a home server last year[dell OptiPlex/i5/15GB RAM, Lubuntu] - found a wonderful voxel game called Luanti (minetest), you can replicate minecraft, or play other games people developed. Minecraft was after my time, but my kids enjoy it, and after setting up a host on my personal server (stupid simple). We been playing as a team, building exploring - find it fun. Isleward a hosted/self-hosted roguelike mmo is next on my setup list, but finding it is more complex to do so.
Also installing a new EQ EMU game, miss EQ.. but live is meh. Not a fan of DBG, who owns it.