We are having a number of problems reported to us around children’s behaviour online – Whatsapp, being a particular problem.
We have been pointed to some useful resources that might support parents with management of online activity. These are at: https://www.internetmatters.org/
Specifically, there are really clear step-by-step guides to control of a child’s device. These are device-specific, for example, this one for an iphone
The other important devices are games consoles https://www.internetmatters.org/parental-controls/gaming-consoles/
Finally there are guides on how to restrict things at the internet service level or tools provided by the isp they can use https://www.internetmatters.org/parental-controls/broadband-mobile/
Pretty much all of these have a nice parent app to manage it from, the child can ask for more time which you can approve/deny (or use as a reason for them to do the dishwasher first).