Becca, I am so excited for you! You're going to have a blast!
So you'll have
diapers covered, but make sure you also have plenty of
baby wipes (useful for diaper changes as well as wiping your hands from a sticky churro or cleaning up some melted dole whip that may have dripped on your shirt).
Bring a
spare outfit for young children. I found I could fit an outfit in a quart size ziplock bag.
Pack a few
snacks for little ones, like cereal or crackers. You never know when they might get hungry. The same goes for thirst quenchers... have a few
juice packs. If you have the opportunity to freeze some, they make great ice packs for keeping non-frozen packs cold, and then later in the day, the frozen ones will melt and still be cool. It's fine to bring a small soft-sided cooler into the park.
Bring extra
ziplock bags... good for leftover snacks, or keeping fastpasses, park tickets, and other items dry.
If you don't want to buy rain gear at the parks, bring along some cheap
ponchos in your bag... they usually fold small. When it rains in Disney, it generally POURS.
Sunscreen. Even if it rains at times, you are in the Sunshine State.
Tissues.
Small hand sanitizer.
Band-aids - kids will be kids (so will the adults)
Small packet of
Tylenol or Advil... just in case (hopefully you won't have a need for it though)
Packets of kool-aid or crystal light drink mix (single servings) are handy too... you can get free water at all counter service restaurants, so if you need a little flavor, just add some mix.
Cell phones or walkie talkies are helpful if you thing your family may split up at any point.
Most important... don't forget the
camera!