Go after the people producing it. Stop bothering service and infrastructure providers. Doing that is either lazy or malicious.
Just because it is bad for you doesn't mean it should be illegal, adults should be able to do what they please even if it hurts them.
So this is a pretty practical solution to protect the kids without infringing on adults freedom per se, because even if some adults lose access, as I said, nothing of value is lost.
OnlyFans is a multi billion dollar company.