Roblox chats are monitored, you can't even type in anything inappropriate or it will cone up as #### in the chat. Most of the kids who play are surprisingly quick to report each other if anyone is being even remotely rude or silly. It's very easy to get temporarily blocked if you are being silly towards other players.
My DD plays a lot and I take an active part in not only learning about Roblox but I also join her 'in game' from my own account so we can play together.
A lot of games are focused on RP (roleplay) so for example, Brookhaven, where you can live in a house in a town and go about your daily life, get a job, meet a friend for icecream etc. A bit like playing with dolls or like the games you play in the playground when younger. In a way it allows kids to continue the gsmes they probably feel too old for in real life. Twilight Daycare for example, where you can play 'mummy' to a baby, feed, change, rock to sleep etc, like you would with a baby Annabell.
DD likes a lot of the cooking games where you basically cook or bake. We ran a restaurant and a bakery together the other week and she learnt a lot about this process, through gaming.
There are 'horror' games like Rainbow Friends where you have to collect items without getting caught by the monsters (not very scary) and you work as a team to complete the collections and finish the game. Some of there horror games might be too scary for younger Roblox players but again, as a parent you can supervise and also set age limits on which games your DC can play.
Roblox gets a lot of bad press on here but I've found it a great way for DD to enjoy gaming safely and also to extend the childhood experience a bit by playing games that are basically a continuation of dolls/barbies and My Little Ponies (yes there is a My LP game too on Roblox).