My wife and I recently took a trip with my then 14 m/o son, my sister-in-law and her three year old daughter. Here are a few of my observations.
1. The baby care centers are a lifesaver. Each park has one and they are staffed for almost every hour that the park is open. These centers are a great place to relax, change diapers, have a snack, play for a little bit. Believe me, they are worth it after your child has been in a stroller forever.
2. My child loved the characters, yours may not, but, if they do, try to meet as many characters at once as you can this saves time later. Camp Minnie Mickey in AK is great for this. You can usually meet Mickey, Minnie, Donald, and Goofy all at once. Pocahontas also makes appearances there sometimes.
3. Sidewalks and streets are very crowded for parades. My son loved them. We had to arrive to our spot at the latest 40 min prior to the parade to make sure we had room for the stroller. If you move at all someone will take your spot.
4. Try watching MK fireworks from the area near Caseys on MS in MK. This gives you access to the baby care center if the fireworks aren't working for the kids. Sometimes they are a little loud.
5. Rides - the best part. You can take your kids on every ride at the MK except for Splash, Space and Big Thunder. If you would like to ride them then use rider swap, just ask the cast member at the entrance for a little ID badge. You'll ride the ride then come back and then while you watch the kids, your significant other can go ride the ride in the fast pass line. Great system.
6. Stroller parking - When you park your stroller, expect it to be moved to a different location. The CM do this so that more strollers can fit in a defined area. They're not trying to be mean, just trying to make more room.
7. Unless your kids really love animals, AK is a waste of time since there is not a lot of rides available for them. The shows are great but can be a little long for little ones. Camp Minnie Mickey saves this park. Don't plan on doing much here. Your kids can ride the safari but the end might be a little fast for them. My son did fine but it was not his favorite by any stretch of the imagination. They may like the petting zoo at Rafikis planet watch. They get to pet a cow, goats and sheep.
8. At HS, there isn't much to do there either. There is the little mermaid show, a little long but not too bad, Playhouse Disney - a must do for your little ones. Your kids can ride Toy Story Mania but actually doing the game will be very difficult for them or for you. The backlot tour is too long for small kids. The great movie ride is kind of relaxing and the kids may like it or not. There are some loud scenes and a couple of scary scenes. Fantasmic - if they can manage some loud noises then this show is great. RNR and TOT will have to be rider swap.
9. Epcot is largely snore territory for toddlers. The seas is a great pavilion for little kids. Talk Turtle and the nemo ride are both great. My son did not like imagination mainly because of the air blown in his face. There is not really anything else that they can do except for Ellens Energy adventure which is quite long.
10. Magic Kingdom - the absolute greatest for little kids. Ride Dumbo first thing if you think that your kids will like it. The order of everything else really doesn't matter. If you are there for breakfast one day, I suggest a pre park reservation, then ride Dumbo as soon as it opens then hop over to Peter Pan, then Winnie the pooh. These are the rides with, typically, the longest waits in Fantasyland.
Adventureland -
POTC - great but a little boring for most little kids
Magic carpets - they tend to like them but a snore for adults, a lot like dumbo
Jungle Cruise - a must do, my son loved the animatronics
Swiss Family Robinson - I'd stay away, there is a lot of climbing and lugging twins around would not be fun with all of those stairs
Frontierland -
Splash - kids cant ride
BTMR - kids cant ride
Country bears - kids like animatronics, what can i say
Liberty Square -
Haunted Mansion - can ride if they arent afraid of the dark, scary sounds or images
Hall of Presidents - great place for a nap
River boat - boring for most little kids
Fantasyland - the best area for little kids
It's a Small World - great
Peter Pan - great but really short
snow White - a little scary, not sure if it is still going to be open when you arrive
Philharmagic - great great great must do
Dumbo - great for little ones
Carousel - well, its a carousel
Winnie the Pooh - easily my sons favorite ride, we rode it, he cried to get back on. Pooh and Tigger were standing outside the ride so we met them there.
Mad Tea Party - Unless they are really steady I would stay away.
Toontown - going to be closed
Tomorrowland -
Space mountain - height requirement
Indy racers - height requirement
Stitch - height requirement and i wouldn't recommend it anyway
Monsters Inc - great
Buzz Lightyear - great
Carousel of progress - great place for a nap
Astro orbiter - very high up, a little scary for a spinner ride
Peoplemover - great place for a nap
11. Make reservations but not for every meal. Counter service increases your time to enjoy the park. Since you will be with your family all of the time, family time isn't the issue.
12. I would suggest a midday nap somehow. There were several days that my son did not want to nap, but we stopped for a rest anyway. This was a lifesaver, especially later at night.
Hope you find this helpful. If you have questions just ask. It is nice to know that someone is bringing their children, the exact same age as mine. My son enjoyed himself, especially the characters. I suggest buying each of them a large stuffed Mickey or other of the Fab 5. This gets them used to what the characters look like.
Congratulations!