When I teach plot to my students, I always use the analogy of a roller coaster. Just lika a roller coaster, a novel starts off slow and builds momentum before finally reaching the apex/climax where the most intense part of the story is. This is the part of the story where our protagonist finally faces his nemesis, overcomes his struggle , or deals with the story's main conflict. After the climax, the action begins to wind down as our author brings the story to an end.
I would say that the boys' rescuing the children from the church is more rising action rather than the story's climax. It is very exciting, however, none of the conflicts in the story are being resolved. The incident is actually adding momentum to our "roller coaster". If we had to identify this story's climax, I would say that it would be the time between the rumble and Dallas' death. There is still lots of action, but the story also begins to wrap up. The Greasers defeat the Socs in the rumble, Johnny passes away, Ponyboy not only realizes that Darry loves him, but that he wants be be just like Darry when he grows up. Ponyboy sees the Socs for what they really are and he and his brothers are allowed to stay together.