parental control on the internet

Over Two/three years ago, I had an idea that web pages could be cert rated like a films. ie PG, cert 12,cert 15 etc.I not saying that the web should be doctored in any way, just that pages could be certed so that if a child tries to access pages that are above there rating they would be unable to. This would allow parent to have piece of mind to known the internet is safe for the children. whilst adults could have access to all internet pages.them being 18 and above. This would be made possible by every user have a separate login, which would declare the child or person age, then a search engine could be attach to the user, that would default to the users age and any pages not certed would not be viewable to the user, who is not the right age, 18 and above. this could be done by inserting cert rating into the page as markup text which the search engine would search for when searching the internet. I known that this system is not fall proof but it could be start in the right direction. I not saying that we should censor the internet in any way for adults, who should be given the right to view what they choose with in reason. but it would give adults piece of mind with regards their children.