I've done it both ways ie with a car seat and without and I'd recommend leaving the car seat behind. The hassle of carrying the car seat through the airport and security, as well as lugging the diaper bag, and then trying to go to the airport bathroom was a nightmare. I was surprised that my son actually stayed in his seat most times as he is very active but a I brought some things to make that happen. A DVD player, lots of toys and took a flight that departed from the States at night so he slept soon after take off. Good luck.