The Wikipedia can be edited by anyone, any time. Even children can edit an article, if they can figure out how to click on the "Edit" link. I daresay my 6-year-old daughter could do it; and would, if sites like pbs.org/kids weren't so absorbing.
However, this is an international wiki. Everyone in the world can see what the child contributes, not just the other kids at their school. If some 44-year-old adult decides to change the child's contribution, it will get changed -- perhaps too quickly for the child's comfort. Well, that's life in the grown-up world, and welcome to it, kid!
On the other hand, a school can have its own wiki. Its students can write booger and fart all day long, and see how their classmates (or the wiki administrator) responds. The lesson might be valuable for them. And with the ability to undo peremptory deletes, a child could defend whatever they deem valuable from techno-bullies.
If I ran a school's wiki, I would allow only signed-on contributors personally known to me. If they didn't follow the rules, I'd kick them off quickly. The word would get around: you can write anything you want, unless you do X, Y or Z. Who knows such a wiki could lead? With the proper guidance, the children might even create something wonderful.
Hmm, my father runs the website for a school in Lexington, Massachusetts. Maybe I'll talk to him about setting up a wiki for that school.
Ed Poor