The internet is not a children's playground
Instead of assuming that a website is safe for children by default, wouldn't it be smarter to assume they're all "inappropriate"? Instead of trying to filter out the dirty pictures (etc), when a child is online filter out everything unless it's specifically marked "safe for kiddies".
The system would work: no one selling porn, sex toys, incorrect political opinions, profanity, etc is interested in children because they are sexually immature (I hope!), don't vote (ditto!), and are likely already experts at swearing. There is no profit in mismarking sites as safe when they aren't.
Parents who are concerned could then install Nanny State software to carry out the universal blocking.
IOW, only let the kids see websites specifically set up for them.
But in truth, we all know that attempts to filter the web aren't really about "protecting the children". Governments detest the free and uncontrolled exchange of political opinions on the web, exemplified by the US government currently having cows over the recent Wikileaks release of classified information. I bet the CIA and its partners in crime would love to have a big red switch labelled "internet" that they could simply flip to the off position.