Suggest a setting change
Parents can see the teen's current settings under Your teen's settings. They can only suggest a stricter setting (for example, changing who can message from Everyone to Friends only).
The teen gets the suggestion, and the setting changes only if they tap Accept. They can also choose Decline. Either way, the parent is notified.
Turning on any of the three Locked settings (private account, messages only from people they follow, less sensitive content) means the teen can't change it.