If you are trying to set up parental controls from within Fortnite on a console (Xbox, Switch, PlayStation, etc.) and you receive an error that says "Sorry, the page you were looking for cannot be found", it is most likely happening because you are within an account that has not been upgraded to a full Epic Games account.
To resolve this issue, please follow the steps in the How do I upgrade a console or platform account to a full Epic Games account? article.
Once your account has been upgraded to a full Epic Games account, you should be able to enable Parental Controls. For instructions on how to enable parental controls, please see How do I set up Parental Controls for Fortnite?