11 and 6yo kids here.

In Android: We use Family Link to approve apps installation and set app time limits per day. No social/user generated content apps. 11yo has access to Edge browser (more on that in Windows).

In Windows: We use Microsoft Family to monitor screen time/usage. We also whitelist webpages that can be visited through Edge (settings translate to Android's Edge).

We only just got a SIM card for our 11yo (so we and family can communicate with her), we closely monitor usage and gave strict guidelines about not answering calls/texts from numbers not in the contact list.