To keep children entertained and well behaved during long airplane trips, buy a small carry on (children's size), with wheels. Go to an "everything is a dollar" store, and fill the bag with "surprises". Have the children carry/roll the bag around the airport etc., and during the flight, give them one surprise every 30 minutes or so. You will be amazed at how entertained they can stay, and perhaps give you a chance to "catch a nap".
Pack an entire day's worth of clothing, a change of clothes, sufficient disposable diapers, and food in a Ziploc bag. Make one Ziploc bag for each day of travel. Each day, one outfit goes on baby, the rest of the supplies go in the diaper bag and you are ready to go.
When traveling with children with medical concerns ... Make sure they have their own identification, whether it be a medical necklace or an identification card. Make sure it has your telephone number, the name and number of their physician, and their medical concerns.
When traveling with children, write down the name, address and telephone number of the place you are staying at on a piece of paper, and "I'm lost, please call my parents" or something of the sort, and make sure your child carries it in his/her pocket/wallet. Tell the child that whenever he or she gets lost, he/she should hand the piece of paper to a woman (make sure your child hands it to a woman, much safer than a man usually!) so someone can help them.
Buy hand sanitizer from Bath & Body Works or Linens 'n Things - it works without water and is perfect for cleaning grimy, sticky hands when you can't find a restroom.
Buy an inexpensive camera (with flash) for children old enough to use it. The trip is then photographed from the child's prospective.
Use baby wipes not only for wiping hands, face, etc., but also for getting out stains on clothing.