Wait until they work out how build sheep fucking machines in Minecraft!
As for Roblox I watch with one eye open and educate them. It's a great environment to learn distrust for others, particularly in Adopt Me. They learned how to not get scammed fairly quickly.
There are a lot of very good, enjoyable games on Roblox. Bloxburg and Bee Swarm Simulator are two fun ones. There are also lots of horrible games on Roblox. Much like all the mobile app stores, you have to look hard and talk to friends to find good stuff.
We play real games now, or occasionally Minecraft mods. The frozen Minecraft adventure mod is quite fun