From a parent's perspective, that's the great part about bubbling it up to the OS user account level.

Its trivially easy to see if the user (child) has indeed created multiple OS level user accounts with different permission levels if you want to spot check the computer.

You'll see it on first startup and then you can have "a chat". With Guest account access disabled, spawning a new account on a computer takes 2-3 minutes, will send emails and dashboard notices to the parent.

Its very much near impossible to verify that the child is not just going to Facebook etc. and using separate accounts and just logging out religiously.

That said I wish Apple/Microsoft/Google had more aggressively advertised their Parental Control features for Mac/Windows/ChromeOS as a key differentiator to avoid Ubuntu/Open Source distros from having to implement them.