Looking at the example of Wikipedia, it needs to be a more substantial and permanent piece of work than a blog. So I would suggest that wikis are suitable for children to collaborate on producing their own revision notes or their cumulative knowledge on a classroom topic. For example, studying the Romans, they could start with an introduction putting them into historical perspective, add a piece about dress, their military exploits, food, type of government and bio pics of some emperors. The wiki could develop over time, perhaps a term or the length of a project. A wiki is to a blog as a novel is to a short story.