Your system would, in essence, ensure that children are not exposed to the very things you believe they need to learn. A curious solution. See 1 above. Parents can make inappropriate choices. So can governments.
Measures begin with exploring the reasons the child in question is visiting the site at issue.
Maybe he or she has questions about racism, sex, etc. I have not, as of yet, had to take anyone out behind the garage and shoot them. But it can also choose not to. Catholics does not make multi-culturalism. That was NOT multi-culturalism, either.