its referring to Dill, Scout, and Jem.
The children want to make Boo Radley come out - it has been their game for the summer. They have heard the myth and gossip about Arthur Radley and are keen to find out for themselves what he is really like.
After the children go to look through the windows at night, Nathan Radley hears the sounds outside and lets off his shotgun to scare them away. in the panic, Jem gets his pants caught in the fence. He struggles free of them and leaves them behind. When he returns to collect them later, his pants are neatly folded onthe fance with the tear repaired.
