KidRex is powered by Google, but uses a combination of tools to make internet searches safe for students. Since NO filters are 100% foolproof, they do have a site removal request form for parents or teachers who see inappropriate material.
Ask Kids is a search engine designed exclusively for 6-12 year old kids. According to their note to parents, each web site in the Ask Kids search index was hand selected as a good site for kids. Ask Kids also adds some fun and games in their searching, which makes learning more fun!
In all honesty, WolframAlpha deserves its own blog post (and will get one soon!) but I really think it needs to be included on this list as well. This is a "computational knowledge engine," rather than a run-of-the-mill searching tool. Check out the video to see how it all works!
Do you have favorite kid-friendly search engines that should be included on this list?