That's a tough one...especially given the age disparity of your kids.
When my kids were little, they LOVED Epcot - esp. the street entertainment, the character meet and greets and the low-key attractions like the boat ride in Norway and Mexico, Figment and Living Seas.
Last year, as somewhat-older kids(9,7,5), they LOVED Soarin', Mission Space, Test Track, Ellen's Universe of Energy...and they still liked the bands, the food and street entertainment...and my youngest still liked the characters. Really...we LOVE Epcot...and it's got such LONG hours it can keep us busy (but not rushed) all day.
Strangely, when my kids were little, they really didn't care that much for AK. It was hot and uncomfortable, and it seemed so crowded. Bugs Life terrified them. They did like the Safari, Linon King and they wanted to spend hours of fun in the Boneyard playground...and the older ones liked Kali. But we were done...and kind of grouchy...by 3 p.m.
In December when we went and my kids were older, we had a much better day...and I am sure if EE was up and running, we would have LOVED that too.
That said...I think if I did not have a park hopper...and I wanted to eliminate a park..AK would get eliminated.
If you get hoppers, you can hit AK in the a.m....see a few highlights (might I suggets - EE, Safari, Lion King and Kali), then head on to Epcot. Epcot for us is just a really all-round relaxing and interesting and fun place to talk and hang out together. I wouldn't miss it.