I first took my girls at age 3 & 5. We did all the parks. Just make sure you have the hopper option because you can really hop around and spend time in each park. You may think your kids will hate epcot, and find that they love it and want to go back. Take advantage of the EMH's at MK!!
My kids have always loved Epcot. Going inside the "big golf ball" was thrilling for them back then. You can do space ship earth, the boat in Mexico, the Maelstrom ( boat in Norway), Ellens energy adventure ( 45 minute ride.. great for a rest and some airconditioning), She will probably like Figments ride in Imagination, and if she is into Nemo, go to the Living Seas, BYPASS the movie ( you do get that option, its really boring!!) and go down to where the cool nemo stuff is. Go see the new Crush the turtle show. It was great!! Honey I shrunk the audience scared both of my kids back then. She will be big enough for Test Track and my 3 year old son loved that this past trip in January. You can take her through the countries and have her make a mask. You stop at all the kidcot spots. Its a great way to have them not be bored while checking out all the beautiful countries. Pooh and Friends are in the United Kingdom inside the store where the kidcot is. There is a character bus in Epcot that stops at certain spots ( check the times and locations on your time guide) My kids still love Epcot. Even my 3 year old son loves it.. the lights in the sidewalk at night, the mini train in Germany, the viking boat in Norway. We spend more and more time there every trip!!
In MGM.. your daughter will love the Beauty and the Beast live on stage show. If shes fearless like my son, she can ride Tower of Terror. There is Playhouse Disney with Olie, Bear in the big blue house, Pooh and Stanley. She will like Voyage of the Little Mermaid too. We eat at Sci Fi every trip and also eat at Pizza Planet too. We go check out Buzz and Woody too!! She will enjoy Muppets 3-d show, the magic raining umbrella, and the Honey I shrunk the Audience playground!! Dont forget to end the day with Fantasmic. Its a must see!!
With 5 days, Id do 2 full days in Mk.. On full day in Epcot, One full day in MGM,( or maybe an EARLY emh park and then hop to MGM for the rest of the day and night) and go early to AK, and hop to another park for the evening. You can take advantage of the night time Extra Magic Hours which will give you an extra 3 hours at a park on certain nights. You will have an AWESOME time!!