I happened to stumble on a page after my own heart: the science of fairy tales. It's a cute diversion for a few minutes, but unfortunately, it's a bit lacking. It only tackles three fairy tales, for one thing. The Little Mermaid one is a stretch (talking about how sound can be captured), though the flying carpet story is fun.
This could be a good starting point for a site teaching science to kids, in fact. Can you spin straw into gold? No, but stars that explode make gold out of other elements. Can beans grow overnight into a stalk that can reach the clouds? No, but kudzu grows a foot a day (I grew up near houses engulfed in that evil ivy), and giants can only get so big before their bones can't support their weight. And as far as the Emperor's New Clothes goes... that one can be taught as is. It's a perfect example of critical thinking in action.