Hi Shelli!
I know that you asked for a book, but at the Moms Panel we get a lot of questions on how to break the news that you're taking them to Disney World.
One of my favorites (since you mention that you're telling them in the morning) is to order the Disney Vacation Planning video and play it for them the night before you leave. It's free! Then, you can order personalized Mickey ears to present to them in the morning. Just put it on their heads and don't say anything. When they ask, tell them "Well, don't you think you're going to need them when we get to Disney World today?" Sit back and watch them flip out!
To order your free DVD please click here:
www.disneyvacations.com. To order the kids their ears, please call WDW Merchandise & Gift Services department at 1-877-560-6477, Monday through Friday, 9am to 5:30pm.
I hope you have a magical time at Disney!