We have done that with a 3 and 5 year old.
Here is what we did:
We fed the kids in the room-once we left the room they wanted to get to the park--not eat breakfast (and it is a lot cheaper)
MK:
1) On early entry days--get there early--fantasyland is still vacant and the kids will more than likely be able to ride most of the rides twice, if not three times before the crowds get thick.
2) Our boys loved Spectromagic and the fireworks.
3) If you do early entry, take a break in the middle of the day--go swimming, take a nap, let the kids run around somewhere--it will make all the difference
4) Attractions they loved:
Fantasyland--everything
Tomorrowland--Buzz Lightyear, Tomorrowland Transit
Authorithy, Indy race cars,
Toontown--everything-especially the Barnstormer
Frontierland--Splash Mountain and BTMRR (they were tall
enough-40 inches)
Adventureland--Jungle Cruise, Pirates, Magic Carpets
MGM
1) Shows/Attractions:
Bear in the Big Blue House, Voyage of the Little Mermaid,
Indiana Jones, Muppets,FANTASMIC (MUST SEE!!!!!), Beauty
and the Beast, Tower of Terror (40 inch height requirement)
AK
1) Shows:
Festival of the Lion King (MUST SEE!!!!), Tarzan Rocks
2) Attractions:
The Boneyard,
EPCOT
1) Imagination-with Figment
2) Making cookies at The Land Pavillion (get there early for that)
3) Running in the jumping waters between Future World and
World Showcase (pack a bathing suit and a towel)
4) Illuminations while eating Funnel Cakes
5) The Malestrom in Norway
Downtown Disney: the
LEGO store--hours of cheap entertainment
Those are what we can remember as what the boys really liked and what stood out both to us and to them. Hope this helps.
Best advice:
If you don't have strollers for both- rent a double stroller--
little legs tire easily
Take breaks--the parks are open late at that time of year and
can get crowded
Plan a character breakfast (Chef Mickey's and
Restarauntosarous are our favorite breakfast meals)
Let the little ones decide what you do from time to time (with
the choices limited to what you give them to choose from, of
course--our boys liked telling everyone how they planned our
vacation
Relax (if that's possible)--your kids will adore you just for taking
them to WDW
Hope y'all have a great trip!