It really depends on what you want to see.
If your kids want to do Fantasyland (Dumbo, Teacups, etc.) you should go there first as these are slow-loaders and are crowded. I would recommend being at the gates right at opening and book over to Fantasyland first.
I would definitely try to get fast passes for Peter Pan, Philharmagic (this is a must see) and Pooh. We usually get a fast pass for one then go wait in line for the other.
Then, if your kids are brave, go to Haunted Mansion, Splash and Thunder Mountains (again, we usually fast pass one while waiting in line for the other), then Pirates of the Carribean and Flying Carpets. If you must, do the Jungle Cruise (it's not one of my favorites...).
Buzz Lightyear in Tomorrowland is a must-see. They will probably also want to do the racecars and maybe visit Mickey's Toontown Fair.
I would eat lunch at either Pecos Bill or Ray's Starlight Cafe...unless you are planning a sit-down...then I would recommend either Liberty Tree Tavern or the character buffet at the Crystal Palace. If you want a complete change of pace, take the boat over to the Ft. Wilderness campground. They have a great buffet that should appeal to all.
The 20th is a Spectro night, so MK will get very crowded in the evening. If you are going to try and catch Spectro, you will need to start scouting a spot about an hour before (parade is scheduled for 7:00, fireworks at 8:00). If you are not going to watch the parade, you may find the ride lines shorter during this time.
Doing MK in one day is a challenge! I just notice you have been to Disney many times, so you are probably going to be fine.
Good luck...I will be at Animal Kingdom on the 20th!