Hi, Leslie!
Welcome to you and all your lovely princesses! Your girls must be so excited to be planning a trip to Walt Disney World!
I would plan to go to each of the 4 theme parks, spending one day at each. With 4 kids, one being a baby, everyone is going to get tired! To keep the group from getting cranky or overwhelmed, plan to take mid-day breaks, avoid super late nights, and maybe do 2 days of parks, take a day off, then 2 more days of parks.
Use your day off to sleep in, swim at your resort pool, and even make that your day to visit the
Bibbidi Bobbidi Boutique at Downtown Disney. Try to make your reservation later in the afternoon after your girls are done swimming for the day, that way their princess makeovers won't immediately wash away in the pool!
Be prepared when going to the parks: diaper bag, stroller, extra outfits for all, snacks, juice boxes, hats, sunscreen, and refillable water bottles. When entering each park, locate the Baby Care Center so you will have a clean and comfortable place for changing the baby.
Be realistic about your trip when planning! With a baby plus 3, you are simply not going to squeeze in everything! Take plenty of breaks, keep scheduled meal times, and make sure everyone gets a good night's sleep. You may not get to see everything by doing this, but what you do get to enjoy will be much more magical if everyone is happy :) !
Have fun preparing for your vacation, and let us know if you have any other questions.