The government should require sites with "unsafe" content to make "safe" versions available (eg force safe mode, readonly, no signup). Sites that are wholly inappropriate for children should self-report so they can be made unresolvable by child-safe DNS.
I'm not saying this specific implementation is the one true way, there's alternatives and ways to work around it. My real point is that the government should have forced sites to implement a consistent method of enforcing child safe mode, that can be easily set in a blanket fashion by the parent.
I'm sure whatever approach will be "too technical" for many parents at first, but once a consistent safe-mode method becomes clear, I'm sure UIs and parental controls will evolve to make it easy to enable.