Hi Stephanie!
Have you ordered the free Walt Disney World
planning DVD? It's a good place to start. I also recommend picking up the book "The Complete Walt Disney World" by Julie and Mike Neal. There are a lot of good tour books out there, but I especially like this for first timers as it is packed with photos and some good tips; the photos help to get everybody excited for the trip and give a glimpse of all of the wonderful things to do inside and outside of the theme parks. If you want more detailed tips and information after reading that book, then I suggest getting 'The Unofficial Guide to Walt Disney World", co-authored by Len Testa.
You're going to be there for several days; I recommend visiting each of the theme parks. All of them are a lot of fun! Generally speaking, I would plan spending 2 days in the Magic Kingdom, 2 days in Epcot, 1 day in Hollywood Studios, and 1 day in Animal Kingdom. Of course, you may decide to spend a day at a water park instead of spending 2 days in a single park. My children, ages 11 and 6, absolutely love Typhoon Lagoon, especially the giant surf pool and the lazy river. The weather should be warm enough when you go! For a recommendation on which park to visit on which specific day, I recommend visiting the independent website TouringPlans.com. They're the research team behind "The Unofficial Guide" and their recommendations are based on a lot of math and years of research. I'm a big fan of their work!
Also, one of the biggest mistakes a first timer sometimes makes is not making dining reservations. Advanced Dining Reservations (ADRs) can be critical if you want to dine in a Table Service (full service) restaurant. You may make on-line reservations
here.
Write back if you have any more questions!