Comment by J_McQuade

I think the correct solution would be to make parents responsible for actually using those controls, as they always have been for controlling a child's access to such materials in other media.

For example, if you have a stack of explicit DVDs and it becomes apparent that your child has access to them, then you will likely get a visit from social services and potentially suffer legal consequences up to and including removal of custody. I honestly have no idea why stuff on the internet is treated differently. Internet providers are already required to check that you are over 18 (much as the person selling you those DVDs is) - if you then share the content that this makes available with a child, then you should be held responsible in the same way. It was sufficient with print, VHS, Sky TV, etc. - why not the internet?