Wow--this is a loaded question. Here's some info to help you get started.
Boo Radley--the children spend much of Part 1 of the novel obsessing over Boo and trying to get a look at him, communicate with him, and make him come out. They judge him unfairly, and it's not until he saves Scout's and Jem's lives that they understand the error in their ways.
Mrs. Dubose--Jem chops down her Camellia plants in a fit of rage, and as punishment, he is forced to read to her every day. It becomes clear that Mrs. Dubose is very sick, and she eventually passes away. While the children viewed Mrs. Dubose as a mean old woman, Atticus tells Jem of Mrs. Dubose's morphine addition and her battle to free herself of it before her death. The children learn that the easy way out, for Mrs. Dubose, would have been to die comfortably while still taking morphine. However, because it was the right thing to do, she chose to break herself of her addiction--a difficult and painful process. Atticus tells the children that Mrs. Dubose is an example of real courage.
Mr. Raymond--Dolphus is unfairly persecuted by members of the town because of his relationship (and children) with a black woman. When the children finally meet him, the discover that though people assumed he behaved the way he did because of an alcohol problem, he keeps company with his family because it's the way he chooses to live his life. (He pretends to be drunk all the time to give people an explanation--albeit a fake one--for his behavior.) Dolphus Raymond helps the children learn not to judge others.
Calpurnia--the children learn so much from Cal. She is a role model for them, and when she takes the children to her church, they see her in a completely different light. (She defends them from Lula, and shows them how she taught Zeebo how to read and write.) She upholds Atticus's rules and values in his absence, and the children love her as they would a mother.
Aunt Alexandra--Atticus's sister is hung up on appearance. She prides herself in being a good hostess, and moves in with the family to teach the children manners and to help them respect their ancestry. Though Aunt Alexandra disagrees with Atticus on many issues, she does become visibly upset upon hearing of Tom's death.
Tom Robinson--Obviously, Tom's unfair persecution shows the children that no one person is better than another. It is clear, even to children, that Tom is innocent. However, because of his color, he is convicted of a crime that he didn't commit.
In witnessing his trial, the children see how cruel some humans can be and understand the injustice present in their society.
Ultimately, the children learn how to respect others from almost every character they encounter in the novel. Though Atticus gives them very wise advice with regard to respecting others, they really learn to value all individuals through their experiences.