Writing stories and then publishing them as a book using your computer is a great activity for kids, They can illustrate their stories and love seeing their name as the Author and Illustrator.
Here is another idea that might excite them.
There is also a site that published kids stories, called Kid Pub
http://www.kidpub.org/kidpub/
Here is their blurb.
Welcome to Kidpub, the largest collection of stories by children on the Internet (and maybe in the real world, too). We've been on the web since 1995, and our database holds just over 46,000 stories written by and for children.
Hope these ideas are useful to you