@Freckles7-
Setting a PIN and requiring it to be entered when adding a channel works when attempting to add via the Roku's user interface.
Unless things have changed recently, adding a channel via a web browser on the Roku Channel Store's web pages bypasses the PIN requirement. Be sure the password for accessing your Roku account is one not known by your children if you don't want them to be able add channels.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X