Having done several rounds with parental control, I'd say -- nfw. We were worried more about timesink than anything else, but over a long period of time, it mainly boils down to knowing your kids, trusting them, with checkups. The tech is just not there to actually control what happens on a device.

White listing worked for a while (months) when they were young, but it was super-high touch and stuff just broke all the time. You try to whitelist a site, but you have to then figure out all their CDNs.

Restricting specific sites works, sort of, until they find some place that hosts that content. Blocking youtube doesn't work(*), every search engine has a watch videos feature. (Why are you spending 3 hours a day on DDG?) There's really no way to segment youtube into "videos they need to watch for school" and "viral x hour minecraft playthrough". Somehow, we've managed to combine the biggest time waste ever with a somewhat useful for education hosting service.

That's leaving out the jailbreaks that come from finding an app's unfiltered webview and getting an open web escape there.

There's basically no reliable method for filtering even on locked down platforms.

* there's probably a way to kill it at the firewall based on dns, but that's iffy for phones and it's network wide.