I am in the same boat as you. My SO and I will only have 4.5 days at Disney when we go this weekend. And we don't even have any kids with us. It never seems like enough time.
For a 5 & 7 yo, I would suggest this (and this could be different depending on your girls personalities & depending on what time your flights are) :
If possible, arrive very early on your arrival day. This might be a good day to do MGM. This park with children that young can be a 1/2 day park. Many of the rides at MGM are geared towards adults. You'll want to see Beauty & the Beast, the Little Mermaid, Playhouse Disney, and the Muppets. But I can't see two little girls getting that excited about Star Wars, Tower of Terror or Rock and Roller Coaster. I also can't see them getting excited by Indiana Jones stunt show.
Animal Kingdom may be more interesting to them; esp. if they like animals. But there are not a TON of rides at AK; it is mostly walk through at your own pace & shows. Perhaps do this in the AM one day and then spend the rest of the night at the Magic Kingdom.
You will want at least a day and half at Magic Kingdom. Magic Kingdom is the park best suited to young kids, IMO. You might want to do a day at Epcot as well.
Epcot is a big park, but with kids that young, you may want to skip Test Track, Mission Space and the Maelstrom; which may be too intense for some kids. (of course, I know some kids that LOVE these rides)
Are you going in early December or during the holiday week? Early December tends to be a very slow time at WDW and I think that will help you a lot because lines will be very slow. Also utilize fast pass on the rides that you can.
If you do 4 days (or even 5 days) at Disney, you will not get to everything, but most people can't get to everything when they do 2 weeks at Disney. There is just so much to do. Hit the highlights based on what your girls like and I think you will be fine.
Missing stuff is just a great excuse to go back!
I would look closely at the rides at MGM & Epcot. Some kids are just bored by Epcot because they are not interested in the World Showcase (my neice, at age 4.5 was bored by WS. She slept through the entire thing). I really think you'll be able to do MGM & AK in 1/2 a day during that time of year.
Another time saver is to eat counter service one meal a day and save your sit down meals for dinners after the parks close. Some people really love Disney dining (I am one of them) but it can take up time that may be better spent on rides if time is short.
Also, as tempting as the gift shops in the parks are, save them till the way out; or just go to Downtown Disney after the parks close to buy souvenirs. It's very easy to end up spending hours in these shops
Seaworld is similiar to AK in that it is mostly something you walk through at your own pace. There are only 3 rides, and two of them might be too intense for the kids, depending on their tolerance of thrill rides. The Kracken is a fast, looping coaster, and Atlantis is a log flume. The other ride is a simulator that takes you over the arctic. I agree though, esp. if your girls like animals, Seaworld is a very nice park.
Whatever you end up doing, I am sure you will have a GREAT trip!!
