In Harper Lee's To Kill a Mockingbird, two incidents below reflect the theme of innocence.
First, when Mr. Nathan fills the hole in the tree with cement, which puts an end to the mysterious gifts that have been left there for them, Jem is the first to notice, and while he talks as if he is comforting Scout, he is devastated. Nathan tells the kids that he did it to save the dying tree. When the children ask Atticus, he thinks the tree looks healthy. However, when Jem repeats Nathan's comment, Atticus backs off, noting that Mr. Nathan would understand the needs of his trees better than anyone. Obviously, though, Mr. Nathan has lied. With the understanding that Boo has probably left the gifts, it shows us just how mean-spirited Nathan is to cut Boo off from the world, even in this small way. It hits Jem especially hard and Scout watches her brother.
Jem leaned on a pillar, rubbing his shoulders against it.
"Do you itch, Jem?" I asked as politely as I could. He did not answer. "Come on in, Jem," I said.
He stood there until nightfall, and I waited for him. When we went in the house I saw he had been crying; his face was dirty in the right places, but I thought it odd that I had not heard him.
Scout is innocent because she does not understand why she can see signs of Jem's tears, but could not hear him crying. The reason, which she is too young to understand, is that Jem is getting older. He cried so that no one would hear; he probably figures he should be mature, and crying so others hear it would be childish.
Jem is older, so he is not as innocent as Scout. However, in Part One of the novel, we see Jem's innocence as he realizes the part he played in helping Mrs. Dubose die free of her addiction to morphine. When Jem gets angry at old Mrs. Dubose's hateful comments about Atticus, he chops up her flowers. Atticus makes him go back, clean up, apologize, and agree to read to Mrs. Dubose everyday. Jem hates it. Mrs. Dubose is very hard for a youngster to take—she can be very nasty. Jem shows what he's made of, acting as Atticus would: doing the right thing.
However, Jem innocently sees it only as a punishment. He doesn't know that Mrs. Dubose is dying. He doesn't understand that his reading has helped Mrs. Dubose focus on something—if not the reading, then perhaps just the sound of his voice as she weans herself off of the morphine.
Mrs. Dubose sends Jem a flower after her death to let him know all is well. Perhaps it also shows him that while he felt he was the only person in the room doing something extremely difficult, that Mrs. Dubose was also doing so. They had more in common that he might have thought—even though it must have been galling to him that he was helping her when she seemed to hate his father so much.
"You know, she was a great lady."
"A lady?" Jem raised his head. His face was scarlet. "After all those thing she said about you, a lady?"
"She was...son, I told you that if you hadn't lost your head I'd have made you go read to her. I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. It's when you know you're licked before you begin anyway and you see it through no matter what. You rarely win, but sometimes you do...According to her views, she died beholden to nothing...She was the bravest person I ever knew."
Innocently, Jem sees his time as punishment. In truth, he was brave, and it gave Mrs. Dubose peace at the end.