When my children were babies, traveling during naptime made sense. It didn't matter the type of travel: car, train, or plane. The kids would sleep.
As they grew out of infancy, the excitement of air or train travel would eventually wear off and they would still go to sleep. So, we booked early morning or late night travel with this sole rationale in mind.
Now, as my kids move later into toddlerhood and out of this stage, my kids become more excited by the fact that they're traveling at a time when they're supposed to be sleeping.
"Mom, we're flying on an airplane...BEFORE 7 A.M!!"
My latest round of traveling has shown me a new Mama Law of travel: When you book your tickets based on the thought that your children will sleep, they will stay awake the entire time.
So, for all of you parents who are planning your summer vacations, think about your own sanity first when booking the travel arrangements. Don't take the early morning/late night travel in the hopes your kids will sleep. Do it only if it's the best time for YOU to travel. Get a full night's sleep, eat breakfast, don't rush your morning coffee as you stand in the security line hoping your kids don't say something inappropriate to the TSA agents.
Enjoy the journey and the destination!