make sure everyone has their own seat on the plane (even the 6th month old. trust me.. a couple hours in a tight space holding the baby while watching the other 2 is gonna makeya wanna pull your hair out). take a small blanket and attach a small piece of velcro to 2 of the corners on one side. the bathrooms on the planes are rather small and make it very difficult to change a baby diaper in them. you can velcro the blanket to the side of the seat infront of you and yours to shield neighbors eyes from having to see you change the baby in your seat.
if the baby is able to eat the little puffs or kixs yet, bring lots of those with you. lots of snacks that any of the kids would eat wether they are hungry or not to keep them quiet.
gum is a must. besure to chew it during takeoff and landings to make the ears"pop" so your head doesnt feel so stuffy.
bring lots of games, coloring books and reading books for you and the older kids. there are little tables built into the backs of most airline seats that you can pull down and play on.
if you are scared to fly, the scariest thing might seem to be the turbulance(where the plane kinda rocks or shimmies in the air) its really normal. just tell the kids and do the same... close your eyes and pretend youre in a rocking chair or on a water bed.
i do this all the time when i have to fly internationally.. it puts me to sleep every time! ^^
when i was little, we went and took an atari with us to hook to the TV in the hotel. Im not sure if big game systems are banned on airlines yet or not, but its something you might wanna look into so that youll have some time to yourself at night to unwind before bed.
as for inside the park...
to avoid the horribly outrageous prices of food/drinks, pack stuff to bring with you.
good things are like pb&j sandwiches, although those tend to make you really thirsty on hot days.
dont bring anything salty and bring lots of fluids and SUNSCREEN!
if you have any specific questions about flying or disney, feel free to send me a private message on here or email me ____@____.com
good luck with your trip and have lots of fun!
ps
dont forget to bring a camera and if its not a digital one, bring lots of film so you dont have to buy any. its over priced at the park.