In Harper Lee's To Kill a Mockingbird, Atticus does not want to tell the children anything about their heritage. Aunt Alexandra, however, believes that as members of a community that should feel indebted to the Finches, Jem and Scout should know "where they come from."
When Atticus comes in to discuss this with them, he is especially uncomfortable. He tries to communicate the sense of pride Alexandra has, but it doesn't feel right to Atticus. In fact, the only relative Atticus has told them about is their cousin Joshua, who tried to kill the president and was institutionalized. The story is something the children would be entertained by, but Aunt Alexandra does not find it amusing—trying to put a different spin on this member of the family.
As Atticus tries to make his sister happy by educating the children to their background and ancestors, the kids feel uncomfortable because Atticus is acting strangely—Scout begins to cry. I believe Atticus acts strangely in that he is not a man to stand on ceremony because his family is well-rooted in the community. Atticus is a real person who does not judge anyone based on who their "people" are or where they come from. Atticus finally gives up and tells Jem and Scout not to worry about it. He jokes a little with them, and leaves the room.