Hi!
You are going to have one adventurous day with that first flight for the little guys!
I recommend bringing a carryon with a change of clothes and anything else you think you will need immediately upon arriving at your Resort. Don't forget when it comes to liquids to only include those in travel size containers due to airline restrictions!
When my kids travel by air they like to have their own small backpack with favorite toys and books. In my bag I usually have a few surprises hiding for the kids that I pull out when it looks like some sort of breakdown is imminent (yes, even my wee angels lose it!). A toy or coloring book that they've never seen before works wonders for distracting them and making the trip smoother.
Also, if you allow them to chew gum bring some along to help ease the ear pressure during take off and landing. Flight attendants are fabulous when they spot an uncomfortable child and coming to the rescue with cookies, but it's a great idea to have your own just in case they need to chew something pronto!
I'm sure that it will all go smoothly with everyone feeling the Disney excitement and I hope that your trip is Magical!