Minetest is a free (libre) similar game, but very mod-centric, with mods loadable from servers without installing them (as easy as Roblox) and (also like Roblox) written in Lua, may be a fun intro to programming if they’re keen to try it (ofc there friends probably don’t play, but a couple boys I know ~7-10 enjoyed it to a kind of harmful level), btw.