Does router setting spply when the child is at school and using data? I do not think so. So you need to have the averager parent setup DNS records and probably pay some subscription to soem people doing the filtering?

It is not easy, if there was just a simple toggle and iOS/Android would ask the parent what kind of religious extremist or prude they are and then do the filtering then sure, but you want a parent to know what a router is, or DNS, or buy some subscriptions for some big tech app?

I agree that parents should do the filtering, but I think big tech should cooperate here, for example I could allow my young child on a PlayStation since Sony did ask the age of the account user and did apply filters in the store and chats.

But what is your objection? Is it really, REALY to much to ask for the Os to ask the birthday of the account user and then the browser to set the appropriate age range flag in the requests? Then the websites can deny the requests instead of the "Are you over 18" popup? Is that too expensive? too dificult? is it too communist?