The entire Moms Panel was lucky enough to see the Candlelight Processional together in 2007. The show lasts about 45 minutes. The Processional is beautiful and can be quite moving if you are a devoted Christian or particularly enjoy Christmas music.
The show features a celebrity guest reader telling the story of the birth of Jesus. This list of 2008 narrators can be found
HERE. The reading is interlaced with Christmas songs performed by a full orchestra and a multitude of choirs. The choirs, which are composed of both professional Disney singers as well as local children's groups, enter the theater area holding single lit tapers (thus the "candlelight processional"). There are significant parts of the show where quiet and stillness would be required. For example during the readings and during songs like "Silent Night."
As I said, many people find the show inspirational. But I personally would not have brought my kids here when they were preschoolers. They would have been too squirmy and I would have been so nervous about their behavior that I would not have enjoyed the show. But only you can be the judge of your own children's tolerance for stillness. If your kids can easily sit through a church service, for example, without complaint, then you're probably fine with them at the Processional. Otherwise, I might save this particular show for another trip.