What do Scout and Jem discuss when they are older?

Harper Lee opens To Kill a Mockingbird with Scout and Jem being older adults and flashing back to the events that led up to Jem's arm being broken, making this conversation part of the things that Jem and Scout discuss when they are older.

In her narration of the conversation, the adult Scout explains that she blames the Ewells for the injury since they were the ones who pinned a crime on the innocent Tom Robinson, and Bob Ewell was the one who attacked Atticus's children as an act of revenge for being challenged by Atticus in the courtroom. However, Jem connects the injury with the children's decision to try and make their reclusive neighbor Arthur Radley, whom they used to call Boo Radley, come out of his home. The reason why Jem connects the injury to events surrounding their treatment of Arthur is because, without Arthur in their lives, Jem would have had much more than just a broken arm--both he and his sister would have lost their lives. This narrated conversation between Jem and Scout as older adults shows just how much they have grown since they were children at the start of the story, more specifically, that their experiences with Arthur helped them shed their prejudices. Their conversation as adults at the start of the novel also parallels a conversation they have as older children the Halloween night they are attacked by Bob Ewell.

At the start of the novel, as children, Scout and Jem buy into the neighborhood rumors and myths surrounding Arthur Radley and  prejudicedly believe him to be an insane person who poses a threat to their lives. However, as the novel progresses, Arthur demonstrates acts of kindness that show the children he is actually a gentle, kind, and caring soul; his acts of kindness include leaving the children gifts, mending Jem's pants, and covering Scout up with a blanket the cold winter night Miss Maudie's house catches fire. As a result of gaining new insights about who Arthur really is as a person, by the time they are three years older at the end of the novel, the children have set aside their childish beliefs in such things as the supernatural and in having neighbors who are dangerous monsters. On the way to the Halloween pageant, one thing they indirectly discuss as older children is the fact that they have let go of their childish beliefs including their prejudices against Arthur Radley.

One way in which they demonstrate they have let go of their childish prejudices against Arthur is through Scout's comment that, though the Radley Place remains a sad and scary looking place, she knows "Boo doesn't mean anybody any harm." They both further demonstrate their maturity when Jem teases, "Ain't you scared of haints?" and they both laugh in reply. When a mockingbird begins singing in an oak tree on the Radleys' property, Jem shows he now associates Arthur with the innocent mockingbird, a bird that only strives to give people pleasure by singing all day long, by saying, "Boo must not be at home. Listen," implying that Boo is not home because he is the one singing in the tree. Fascinatingly, their conversation as older children about their rejections of their childish fears and prejudices happens the same night the children are attacked by Ewell and rescued by Arthur. More fascinatingly, their conversation as older children at the end of the book concerning their rejections of their prejudices against Arthur parallels their conversation as older adults at the beginning of the book, similarly about the rejection of their prejudices against Arthur, bringing the book to a full circle.

Hence, it can be said that the things Scout and Jem discuss, both as older children and as adults, concern their rejections of their fears and prejudices, showing us just how much they have matured throughout the story.