It is absolutely beautiful, but not very interesting to small children...even if you bring toys and great snacks. There are also some very loud horns. My kids made it maybe 20 minutes at 3,4 &5.
You can stand in a long, long, long line to be seated, or can get special seating w/a smaller line w/a dinner package. I believe the time of your meal determines which show you will get the seating tix for.
The theater is at the American Pavilion at Epcot. You can also hang around the American Pavilion to hear the show and see glimpses of the performance.