Here are some tips:
Don't overschedule! This is a classic mistake all parents make. Set up an agenda but be flexible enough to give up something you really want to do if your kids need some rest or downtime.
Have your kids help in making an "entertainment bag." My kids coined this phrase as toddlers and still use it in their teen and pre-teen years. This travel bag includes items they have selected which fit into a backpack or carry along. A special lovey, small items such as post-its, stickers, pencils, small sketch books, etc. Our local library even lends small MP3 players with an entire book selection on it. You can also allow them to select small snacks to keep in their bags. As long as it's light enough for them to carry, it's perfect.
Stop for breaks often. While not possible for airline travel, on a road trip, a break where kids can stretch their legs is invaluable. For any kind of travel, have your kids burn off some steam before they board. My kids loved "how many times can you ride the people mover in the next 5 minutes?" or "how many wall push ups can you do before we get in the car?" A little healthy competition will serve you well before a long trip.
Pack healthy snacks. I know that your kids have already packed some snacks in their entertainment bag, but it's also best to pack foods that have staying power, i.e., heavy on the protein for your travel. Nuts, string cheese (stays good longer than you think) and beef jerky are all good choices. Because kids tend to get a little backed up during travel, it's always good to have some options with fiber as well. Fruits as well as cut up carrots and cucumbers are helpful. Plenty of water is required and consider the bathroom breaks a good reason to get up and stretch your legs. If you are road tripping, bring a cooler.
Novelty. If you have younger kids, or even older ones, surprise them with a book they've been wanting or a snack they love. I once brought heart shaped post it notes on a plane and my kids spent the entire flight making designs on them and sticking them to the windows.
Be mindful of cabin pressure. If flying, making sure to bring along bottles with drinks that toddlers can suck on as well as pacifiers. Nursing moms will want to do so during take off and landing. Those times can be especially uncomfortable for little ears.
Share your itinerary with your kids. This little tip can prevent many a tantrum. When they know what's happening, they feel more engaged and prepared. For the kids who can't yet read, draw them a picture of what will be happening. This is especially helpful for kids who are anxious.
Offer activities that include "heavy work" and oral sensory input. Think play doh, pop beads, clay, a hole punch. These provide little hands with opportunities to move, even without necessarily moving their bodies. Similarly, a little chewing gum or fruit leather keeps little mouths working and occupied.
Fidgets. Items like squeezy balls, finger knitting, drawing faces on the pads of their fingers, finger play games...all are not only great for them developmentally, but pass the time pleasingly.
Lower your expectations. Things happen, even when you have spent a year planning for the trip. Don't let yourself get derailed because you had to cut the day short at a water park because your child was exhausted. You and your kids will have a much better time if you go with the flow. You'll be able to relax and watch the kids have fun and your kids won't worry about letting you down.
Have a great trip & send me a postcard!