There are parental controls, but it’s rare. FOSS projects usually aren’t very keen on building systems of authority, even parental ones.

For smartphones check out /e/OS (Murena Smartphones). They added parental controls recently, not sure how good those are though.

For computers your best bet’s probably a Linux with Gnome. They also added something recently.

You might be able to combine both with a custom DNS service, surely there’s something out there for that usecase. But that’s already getting pretty complex.