I've gone to WDW my son was 2 and then when my daughter was only 5 mo.
Both had its challenges, but both trips were fun.
My general advice while there:
1) Manage expectations - just plan on going slow and plan on doing stuff only they can go on. Yep .. you'll have to skip some fun rides unless you want to go solo.
Know you can't do it "all".
2) Plan on going early (rope drop) and napping in the park in the early afternoon (or going back to the hotel since you are so close)
3) Plan on ending your day early (not later than normal bedtime) . it's tempting to want to see Fireworks with the kids, but that is a late night for ones that little, especially if you want to get up early the next day. We've enjoyed them just fine from our hotel as we are tucking them into bed.
4) Fast Pass whatever you can .. even if it "planners" or guides tell you not to because it is traditionally a short wait time. ANY line skipped is a good thing with a toddler.
5) Get your Fast Passes ALL for the morning and all in the same general area of the park (don't criss-cross the park trying to use Fast Passes). This leaves your afternoon flexible (key for a child that may be wiped out by 1:00 PM) and let's you get Fast Passes "on the fly" for a ride nearby potentially.
6) Avoid "scary" rides (and be aware that what you don't consider scary . they may find frightening) .. We avoided rides like Pirates, Haunted Mansion, etc to avoid crying on the ride and/or nightmares later.
7) Stop and smell the roses .. get pictures at photo spots, go shopping, stop and see street shows .. let them dance at dance parties. if they vocalize their favorite ride .. go on it again and again!
8) Do a character meal - a great way for a little one to see characters without waiting in line .. and it doesn't cost any extra for them (since eat free at buffets).
9) Don't let friends/family inevitable "guilt trip" (You are taking them that young . they won't even remember) bother you
Other tips:
1) Take plenty of snacks, water, etc.
2) Bring a good backpack to be the diaper bag.
3) To lighten the load, bring a bag of emergency stuff (like a change of clothes, extra diapers) and rent a locker.
4) Rent (since you are flying) (via 3rd party sites) a good stroller that reclines all the way flat and has good shade/coverage. It's easier than bringing your own on a plane. They deliver it right to your hotel.
5) Prep your child - show them Disney videos/shorts (maybe even whole movies) of Disney characters the would see in the parks so they "recognize" them in the parks. It will make it way more fun for you and them. Disney Junior shows, Winnie the Pooh, etc. A lot of age-appropriate things for children that age.
And most of all .. Disney World is MAGICAL for kids .. even THAT young .. enjoy them enjoying seeing things.