On flights shorter than 3 hours, dress your children in a one piece with footies. This way she is comfortable and if it is a little chilly on the plane, you can always take an extra light blanket.
In flights longer than 3 hours, be sure to carry at least onesies, along with little pants and two pairs of socks. Also- and this is key- be sure to look behind you when you disembark. I cannot tell you how many tiny little socks my baby has offered to the airplane gods!