Of course Roblox have more player, but does your child really need millions of players?

It's the same network effect with other megacorp, we could argue the same about X/Instagram/Mastodon, the question could be changed to: Do you want your children to be groomed to use closed source ecosystem from shady companies or do you prefer they gain experience in using relatively open ecosystem ?

Luanti let you make multiplayer games/mods too. For Minecraft there way to play outside of Microsoft sanctioned versions and servers.