Check baggage guidelines. The rules are always in flux, so before packing anything, call your airline to find out the maximum size and number of bags you may carry on. And then still be prepared to check something at the last minute -- know which bag you can live without during the flight. In the bag you know you can't live without, pack a change of clothes for at least the kids, if not the whole family. Remember that backpacks are a convenient, hands-free option for parents. Know the weight limits for checked bags, too -- you may think you're doing yourself a favor by packing for your family of four in one suitcase, only to find out at the airport that you're way over your checked items weight limit for a single piece of luggage. Rules vary from airline to airline, so call the one you're flying for the up-to-date info on limits. You may find it useful to drag out your daughter's petite Minnie Mouse valise after all.
Don't wear big coats. Pack bulky jackets in your checked luggage -- that's one less layer you and the kids will need to remove for security.
Don't carry gifts. Don't bother trying to carry on wrapped presents -- they'll be opened. Put what you can in your checked bags or ship gifts in advance, especially any that contain liquid. The 3-ounce container rule applies to presents as well.
Be ready when you get to security. Your stroller or car seat will have to go through the x-ray machine, so take kids (and all their stuff) out in advance. Any child old enough to walk may be asked to remove his shoes -- you'll want to make sure they're all in something easy to slip off, so leave the lace-up high-tops at home. If you're traveling with a nonambulatory babe, you will be asked to walk through the metal detector carrying him.