Hi, Mel! To begin, you can purchase your tickets for the theme parks either online before you go or when you arrive at the ticket window. I would say it saves some time to order in advance, which is definitely a consideration if you are going to be conscious of your time.
If you are hoping to snag a reservation at a table service meal, including character dining, you'll want to book that as soon as you can. You can make the reservations online at
Disney World Dining. You can search for meals available at the theme park you are visiting. The character meals in those two theme parks include Crystal Palace and Cinderella's Royal Table at the Magic Kingdom, and breakfast and lunch at Hollywood and Vine at Disney's Hollywood Studios.
I'd probably make a list of the must see attractions for your family. You can find information on each theme park at
Walt Disney World Theme Parks. That will help you plan your itinerary for each day.
If there's anything else I can do to help you get ready, you can find me right here!