We have traveled a lot with our 5 and 2 yr olds. I have one who won't sit through a movie. These are some of the things that we have done.
Make sure you have some new toys that they haven't seen before. (Need to make sure that they won't make a mess or have little pieces, something that will hold their attention for more than 2 minutes. It just depends on what your child likes to do.)
Lots and lots of snacks!!! I always bring lollipops. They last a long time, keep my kids quiet because they aren't used to getting them, and help them clear their ears on take-off and landing. Downside, they are messy. Bring babywipes. Also, bottles/sippy cups are good for ears.
Make sure you have the bottle/sippy cup. Those little airline cups they serve drinks in are perfect for spilling all over you or the person next to you.
Bring their favorite comfort items. For some kids it is extremely stressful to travel and anything that helps them be calm is helpful. My younger one used to always get a fever when we traveled.
I have a pile of toys that are great for traveling in a cupboard that I try not to take out much when we are at home. Things that work for us are Doodle Pro boards, books, magnetic/felt scene boards, stickers.
Depending on your child, I used to spend most of the time walking up and down the aisle. My first child HATED to sit still. Most of the time the flight attendants are nice about it. Just ignore the ones that aren't. Same with the passengers. :) I wish you good luck and, maybe, you'll get lucky and they'll both sleep. It happened to me once. :)
