Hi Julie,
How exciting that you are planning a family vacation to Walt Disney World! You've already got a great start by narrowing down when it is you want to travel. My suggestion would be to travel either early May (before Mothers Day) or early June (at least a week after Memorial Day). By mid-late June the heat and crowds begin to pick up.
Once you've decided when to go, now it's time to start thinking about accommodations. There is a wide variety of resorts at Walt Disney World, so I am sure you will find something that will suit your families taste and budget. My favorite website for browsing the resorts is
www.allearsnet.com Simply go to the accommodations page and you'll find a complete list of all the resorts with detailed information and wonderful photographs. It's always great to have a backup-resort in the event that your travel dates are inflexible.
Before booking your vacation, you will want to consider theme park admission ticket options, as well as dining plan options because you will be asked about it by a friendly cast member when calling to make your reservation. Disney has made it incredibly easy to roll all these decisions into one easy package. Use this handy
Vacation Booking Guide to learn more about these things. For a first-time visit, I suggest at least one day per theme park (there are four) and an extra few days for a waterpark or to repeat the parks you will most likely enjoy the most.
So once your trip is booked you can concentrate on planning the day-to-day schedule of your visit. When you're ready there is lots of great information here on the Moms Panel regarding parks and restaurant options.
I hope this helps!