We took our children from So. FL to NYC to visit my in-laws the Thanksgiving of 2001, just after 9/11. My husband was too nervous to fly, and we opted not to use the tickets we'd purchased 6 or 8 months prior to our trip. We rented a mini-van, and off we went. Our youngest was 7 weeks old, and our oldest was 26 months old. We rose early, and drove from 4 am on. We stopped at the first rest-stop after they both woke up, and every couple of hours in between, keeping in mind where the next rest-stop was (10 min away or an hour), and stopped accordingly, erring on the side of caution, and stopping more, rather then less. We made it in two days of driving. I brought tapes, the foot rattles that go on like socks for the little one, and nursed as soon as he started to become hungry. He stayed in his carseat, and I climbed in the back with him and leaned over. As soon as I needed to start nursing, my husband pulled over at the next rest-stop. I also tried to anticipate when he'd want to eat, watching his cues closely, so I didn't have to nurse him in his carseat often. He NEVER came out of his carseat unless we were stopped at a SAFE spot. The only exception I would/will ever make to this rule is if his immediate health and safety are severly at risk (ie choking, turning blue, etc.). I'm a NICU nurse, and my own babies are the most important babies I've ever cared for, as they are my responsibility, and the oness falls on me. I also found that bringing a blanket to lay on the ground, and let the baby have some time to play at the rest stops really let him get hsi wiggles out, and even tired him trying to crawl and roll over. I must say, some babies travel better then others, and you may not have as smooth a trip as some, just be FLEXIBLE, and have a lot of extra time built into your travel time.
Keep in mind, travellers of the night, that your reflexed will be slower then during the day, and a tired driver is worse (less safe)then a drunk one on the roads...
They were done with the car and driving once we arrived, and didn't have to go back in much once we got there. THe trip home was also smooth, but took a bit longer.