How exciting to be a first-timer and congratulations on finding The DIS before your trip. I guarantee you - you will get a TON more out of your trip with your research here.
I brought an almost-2 and 3.5 year old last Sept and will be bringing them again at almost-3 and 4.5 this year. I am so excited for this year because I can already tell how much more the younger one will get out of it.
First of all, let me start with general tips: Be flexible and try not to be disheartenend if your little ones aren't as 'into' it as you'd like them to be. My dd (the almost 2 year old) didn't even like the Winnie the Pooh ride last year - so I was surprised. You just have to go with the flow. Also, with little ones and older ones, make sure you learn all about child swap (do a search in Theme Park board and you'll find a ton) and try to have a plan (are you going to let the older ones separate some of the time to do more adult things, etc. - probably a good idea to decide some of those type things upfront).
Now, this is what my kids liked and I expect them to like for this trip:
Magic Kingdom: Winnie the Pooh, Carousel, Dumbo, Goofy's Barnstormer, Splash Mtn, Buzz Lightyear, Donald's house, playground across from Donald's boat, Spectromagic parade
Animal Kingdom - THe Boneyard playground, Safari, Donald's Breakfastosaurus
Epcot - Turtle Talk with Crush, Maelstrom, all the games at Innoventions
MGM - Playhouse DIsney Live, Honey I shrunk the kids playground, Muppets, Beauty and the Beast stage show
The little ones also loved the spray jets at our resort Pop Century. Not sure where you're thinking of staying...
You'll have a blast!