The first theme that I can think of relates to the wisdom of children, particularly Scout's wisdom when she confronts the lynch mob facing down her father at the steps of the jail. Scout is only a child, but her innocence is changed to an extent this summer as she sees the way that grown-ups behave. However, she retains enough childlike simplicity to make these men reconsider, for the moment, their actions. Atticus states in chapter 16:
So it took an eight-year-old child to bring 'em to their senses.... That proves something - that a gang of wild animals can be stopped, simply because they're still human. Hmp, maybe we need a police force of children.
Another moment in the piece that also relates to the wisdom of children is when Atticus emphasizes the imporyance of telling them the truth. He shelters Scout and Jem by protecting them, but he also is honest with them, for children have the wisdom to tell when adults are lying. He states in chapter 9:
When a child asks you something, answer him, for goodness' sake. But don't make a production of it. Children are children, but they can spot an evasion quicker than adults, and evasion simply muddles 'em