I completely agree with jwann. I have 4 boys who have grown up going to WDW & they all like something different. No. 3 son has never liked AK since it opened. He goes if we ask him to, but usually opts to stay behind if there is a way to.
The younger they are the more they will love MK, but at this point, with my youngest being 13, we pretty much do MK in 3-4 hrs. & they've had enough for the whole trip. I remember spending entire days/nights there when they were younger.
My kids have always loved MGM, but they also like roller coasters & fast moving things (ToT). They love the studio tour & the Muppets, as well - even at 13 & 18yo.
I remember thinking EPCOT's World Showcase was boring when I was younger - now it's one of my favorite places to be. However, my kids only enjoy going into 2-3 of the countries & then are itching to head into Innoventions, Mission Space & Honey I Shrunk the Audience.
Again, it's all in what your kids like. I also recommend getting one of the books to research the rides & attractions. With good planning you can cover everything in every park that you/they want to.
It was good advice from the others to split up your days. We ALWAYS start at one park in the am & move to another in the afternoon. Depending on what's going on & the day - sometimes it's 2 parks a day - sometimes it's 3. We just rotate it back & forth depending on shows, fireworks, weather, etc.