It’s a way of socializing the losses, this time you lose civil liberties and they get to keep acting unrestricted
The correct solution that does not do this is to put liability on the parents.
So if your goal is for the state to decide what is good or bad for children, then yes, giving parents fines when their children access 18+ content will motivate those parents to parent their children. That will be an effective way to achieve your goal. Other policies have issues with externalities (ignoring the inherent externalities of creating liabilities ex nihilo, which will exist no matter what policy you choose).
If you believe that parents should get to decide what content their children, then like me, you would oppose any kind of legislation with this goal in mind.
And, like most such policies, will disproportionately impact the working poor.
I guess we made a mistake in not consulting the oracle of all legal matters. Very sorry, we will consult you on all future proposals.