A good news for all the parents out there. Don't waste hours looking through websites trying to find the ones that are kid-friendly. Today I came across a search engine just for kids called KidRex While no filter is 100% accurate, this is a great place to start.
KidRex

KidRex is basically a kid friendly front-end for Google searchers that uses Google's SafeSearch technology to filter out child-inappropriate content. I hope that all the parents and teachers start using this search engine on top of all the firewalls. It's a great way to let the kids use the good side of the internet.