Unless your trip is only for a few days (say 4 or less), then I'd actually take more stuff, skip doing laundry, and check the bags. I'd then only bring a small carry on (or share the largest size carry-on allowed between the 3 of you) for esential stuff that you don't want packed, like medication and valuables. You should also pack in the carry-on a change of clothes, your toiletries, and anything else you can't live without for 24 to 48 hours, in case the airline loses your bags.
This is just me, but here's why I check when I have a long trip:
#1. You are on vacation. Vacation = fun. Vacation does not = doing chores normally done at home, such as laundry.
#2. Allows you to bring more clothes, more shoes, more of everything really. This can save you money if you need something that you didn't bring. With more clothes, you have more options if the weather isn't what you'd planned on, or if suddenly you decide to do something that requires you to dress up or down more that what you'd planned on when you packed.
#3. It's easier to make sure you have more space to bring home all the stuff you're going to buy. I always try to bring an empty duffle bag with so I've got room to bring things home. But the empty bag still takes up space in the normal luggage. That in turn, displaces stuff I planned on bringing, so I wind up either needed a bigger bag or cutting down further what I'm packing.
#4. No dragging stuff thru the airports. Especially true if you have connecting flights. 'nuff said.
However, if you still want/need to travel light, here's what I would do.
#1. Bring stuff you can easily re-wear with out washing (so long as you kept it clean the first go around). Jeans do this very well, for example. This will help cut down on a) the amount you need to pack and b) the amount/number of times you need to do laundry.
#2. Still bring enough underwear to last the trip. It doesn't take up that much space, anyway, and there nothing worse than running out with no time to wash!
#3. Bring a small bottle (and I mean very small, empty out a sample size shampoo bottle and re-fill it) of liquid laundry soap. A few small things might be easliy washed in the room, saving you a trip to the laundry room. You only need a small amount, a little dab will do ya!
#4. Pack everything you need for the stay in Florida in the bigger suitcase. Put the things you'll want on the plane in the backpacks (but since there are 3 of you, you may be able to put all the stuff for the plane in one of the back packs, leaving the other two for more clothes). The suitcases will be in the overhead, but the backpacks are under the seats and easily accessable. I use my little backpack to carry my cd player and cd's, my book, snacks, and travel pillow. Even with the seatbelt sign on, I can always access whatever I want from my little backback without getting up! Very handy! I also double the outside pockets of my backpack as my travel purse. It has my wallet and my house keys. This makes it extra important NOT to lose this bag, though! Also, I've just recently started to carry a very thin man's wallet in my front pocket for time when I just need I.D. and money and don't want the hassle of a purse. This way if I lose the backpack, I've only lost my cd player and book, not my money or drivers license.
Whatever you choose, you'll be in WDW, so you'll have a great time no matter what! Good luck!
