The point isn't to make it impossible for children to ever get to the
pages. The point is to both advise parents as to the contents of pages and
give them some tools to control their children's access. 'R' movies don't
mean that children may not be admitted. It means that parent's (or at least
an adult) must make the decision.
In my little idealistic world I would probably choose monitoring over
control. That is to say I would want to be able to see where my children
have been so I could talk to them about it if they went somewhere that
needed some explaining. But that coming from someone who doesn't have
children and isn't planning any.