[Windows Central Question]

Kid logs in with a microsoft account which can be monitored, but then creates a local account that can't be monitored and accesses internet sites that are not appropriate

[realwarder]

Only admin users can create local accounts. Don't make your kid an admin user.

[TexasLabRat]

Make sure the account is set as a "child" account in the Microsoft Family stuff (for monitoring/filtering/etc), as well as a "standard user" locally (rather than administrator) so it does not have administrative access to the add user tools. It seems to be possible to have a child account still be an admin locally on a device so you have to make sure both things are set properly.