I would suggest https://en.help.roblox.com/hc/en-us/articles/203313390-My-account-was-hacked-What-do-I-do- but they actually decided to delete my account and bar me from accessing my own data.
Kids will do dumb stuff on ROBLOX. If you want to prevent that you can dress up with the free items roblox has in the catalog. If not they should just ignore the hate.
You Click The Sign Up Button And Type In Your Username, Password For That Account And Birth Date In The Boxes On The Website. And then click you agree with the terms of service. Then click the green sign Up Button.