Turtle Talk with Crush begins at 10:00, so I suggest being at the Living Seas at 9:45 and get in line. The theater has limited capacity and the line gets longer later in the day. What can you do before that?
-- Spaceship Earth, or
-- Living with the Land or Circle of Life, both in the Land pavilion.
There are several "play" areas your children would probably enjoy.
-- Innovations East and West have some interactive things to do, and are fun for kids to explore.
-- At the end of the Journey into Imagination there is another similar interactive play area that you can use whether or not you go on the ride.
-- There is a Viking ship in the Norway pavilion that kids can play on (closes at dusk).
Other kid's stuff:
-- Each country in world showcase has a "Kidcot" station where CMs help kids with hands-on activities. Many of the countries have character greetings, see
http://pages.prodigy.net/stevesoares/ for details.
-- There is an outdoor model train display at the Germany pavilion. No touching but fun to watch!
-- They would probably enjoy riding the boats across the lagoon -- simple but fun. If they REALLY like it, you can exit at the International Gateway and take a boat ride to MGM studios and back!
-- Don't forget the Baby Care Center in the Odyssey pavilion between Future World and Mexico. The perfect place for nursing and/or changing diapers, air-conditioned and relaxing.
-- Energy Adventure is OK but you should be aware that it lasts about 45 minutes from start to finish, and only about 15 minutes is dinosaurs. The other parts may not be interesting for small children.
-- If it fits your budget I suggest making lunch reservations at Garden Grill in the Land pavilion. A character meal with Mickey, Chip n Dale, and Pluto in a revolving restaurant. Good food too!
-- Epcot is huge and you just about have to have a covered stroller for young children. You can rent a double stroller at Epcot if you wish. It's a big plastic shell but works fine; I think it's about $18 for the day.