My two teenagers are still Roblox enthusiasts and it is full of games people have created including First Person Shooters, Fortnite knockoffs, dating games, etc. i do think there is some oversight and the 8 bit graphics limit how realistic anything is but there is content that parents will find objectionable.
Also, Roblox does not allow voice chat under 13 so make sure your elementary school kids are honest when signing up and that they don't have accounts you don't know about.