Answer:
After they saw that the church was on fire, they asked what was happening. They realize that they most likely set it off with their cigarettes and children could die because of their mistakes, so Johhny and Ponyboy run inside. They save the kids, Ponyboy gets out of the church, but Johnny's still inside. The church starts crashing down as Ponyboy saved the last kid, and suddenly Johnny screams. Next they're in the ambulances.
If you wanted more or something more specific, just ask! I didn't really know what you meant so I summarized it. Have the book right beside me! :)