Cindy,
My daughters are just around that same age range (8 and 6 now), and so I think I can help.
While Epcot does not have as much for younger kids, you certainly can make a day of it. There are a few good attractions in Future World. My girls' favorites include
The Seas with Nemo and Friends,
Soarin,
Turtle Talk with Crush, and
Test Track. The two sides of
Innoventions also have some fun exhibits that are interactive and let them feel like they are running the show. They really loved the Great Piggy Bank Adventure last time.
As for the World Showcase side, there really are not many rides, though I like the
Gran Fiesta Tour in Mexico.
Agent P's World Showcase Adventure is also fun for them, though make sure they each get their own communicator. Sharing is not as much fun on this project. And if your girls are outgoing, the
KidCot Fun Stops are great, as they get to do some crafts and meet young cast members from around the world.
Since you are having a big breakfast there, you might skip a big lunch, but take them to a fun table service restaurant in the World Showcase. There are some that are fun, and they help open them up to a new culture. I am a huge Epcot fan, so if you need more ideas, write me back and let me know.
Have a magical vacation!