The only way to protect kids from the internet is by separating them from it. Consider Wikipedia, one of the sites that is pretty much guaranteed to be on a whitelist of websites for children, yet it is chock full of porn. In fact, an entire copy of "Debbie Does Dallas" is hosted on the Wikimedia servers, not to mention the images that show up on the articles for sex acts.
Even fixing those issues, children will still find porn on the internet and kiddie fiddlers will still be able to contact them. Nothing in the universe can stop a 13 year old boy from getting access to porn. Leave a boy alone for a couple hours with even a completely disassembled machines with no networking, modems, or even any other connection and in no time, that machine will be up and running and connected to several porn sites. As for the predators, the law and society has pushed them so far underground that by-passing filters and exploiting weak points in child-protection software is second nature to them.