The advice you have received so far is great! I think you are wise to break EPCOT into two visits.
I would like to give you one more option to think about. Instead of dividing EPCOT into a Future World Day and a World Showcase day, consider doing a "left side" and "right side" day. For example the first day, you enter and after riding Spaceship Earth (if it's busy save it for the next day) you go to the left and visit: Test Track (for those tall enough), Wonders of Life Pavilion and Ellen's Energy. Then instead of going back across to the other side of FW, go do the "left side" of WS. Visit - Mexico (a cheesy ride, but kids like it and it is cool and dark and relaxing), Norway (another boat ride, one kind of scary part but not really - they try to make you think you are going over the edge of a water fall, but you stop and backup) - you can skip the movie at the end if you wish; China -they may not be ready for the movie, but they have a lot of acrobat shows here; Germany, Italy and American Adventure (another show that is dark and cool! The show is great, but maybe kids your age won't find it very exciting - great time to take a nap!); Japan, Morroco and France .
Then duck out the International Gateway and take the boat to MGM.
On the day after you've been to AK do the "right side": The Living Seas, The Land, Journey Into Imagination (the 3D show here can be intense), Canada and the United Kingdom. If you didn't quite see everything in WS on the first day finish it out then back to the International Gateway to...maybe to Beaches & Cream Ice Cream Shoppe at the Beach Club Resort for something yummy before returning. If you are staying onsite, you can catch the BC bus to Downtown Disney and then catch the bus back to your resort (unless you are a Boardwalk area resort then you can walk or ride the boat!)
This way it isn't ALL world showcase on one day. Don't get me wrong, we LOVE Epcot and my kids have from the first. They have always enjoyed the Kid Cot Stations and yours probably will also. But a full day of WS may be a bit much for them at this age! They may be yelling, "HEY! Where are the rides?!?!"
Just a thought!
