I haven’t seen an English version of this yet, but I found this site interesting: WikiKids
It’s sort of a Wikipedia for and by kids. The project is still in the beginning stages, so there isn’t much content on the pages yet. What I like about this site is that there are good instructions for kids and adults (teachers etc.), and that the site is very kid-friendly. It also seems that there will be some level of moderation (just like Wikipedia). I really think this site has some potential for education. The real trick is going to be to keep it as open as possible for kids to use, but at the same time not too open so that the site becomes unusable.