Tikatok is a new site where kids can write and illustrate stories -- and then have them published for a fee. I can't decide if this is a good idea or a bit of a money-grab. The writing program looks good -- it's got lots of prompts for children who get stuck -- but I'm not familiar with the other writing programs for kids that are out there. And if you want to publish one of your kid's stories in book form and handmade isn't good enough for you, there are already a couple of sites out there (like blurb) that print nice-looking books.
And here's a site, MagCloud, that allows you to publish your own magazine. They even take care of mailing and subscription management.