Kerpoof is one of my new favorite sites for budding authors. The Disney-owned site is surprisingly non-commercial, and it's really and truly FREE to use. The registration process requires a parent's email but in my experience, I can honestly say I haven't noticed any spam as a result of our use.
Why I like it: the storybook feature gives kids a chance to create their own illustrated books online, and as a bonus, they're getting great keyboard practice at the same time.
If you need to take your kid to the office this summer, I highly recommend sitting them at the keyboard and sending them to Kerpoof. Then, make sure you take a break to read what they're writing. You just might find you've got a talented writer in the family, and the next thing you know, you'll be sending out query letters and learning all about the publishing industry.
Hey, worse things could happen. :D