It is difficult for parents to do this today! You can either have a limited set of apps with no general internet access (fine for younger kids), or domain-list filtering which takes significant work to set up, has many false positives and negatives, ie it's both a chore to request/allow useful things, and easy to get around. Lawmakers have been convinced the solution is opt-in, so websites can self-categorize and nothing needs to be configured on device – and I agree that websites need to self-categorize, but then this would make it very easy to reliably filter on device.