Why wouldn't Dally go into the church for the kids, but he did go in for Johnny? Dally didn't know any of the kids, so he didn't feel the need to save them.

Ponyboy passed out when he came out of the church, so Dally had to go in to save Johnny because no one else was going to save a greaser.

Dally knew that Johnny and Ponyboy didn't need his help to save the kids.

Johnny is family to Dally, and he would have done anything to save him