In To Kill a Mockingbird by Harper Lee, Jem, Dill, and Scout begin to invent a game which is based upon their imaginings and rumors about the Radley family. Like most children, Scout, Dill, and Jem use their often times overactive imaginations to invent foolish games that involve dares and deeds of daring-do. They know bits and pieces of Boo Radley's past, and wish to draw him out of the house to show that they are not afraid of any part of the legend that is the Radley house.
However, the "Boo Radley" game has two purposes, one of which is not apparent to the children or to Atticus until the time arises for Boo to come to the rescue of the children against the attack from Ewell. In the meantime, before this attack comes into play, Atticus warns the children to stop the game entirely, stating that all people are entitled to their personal privacy. This is good parental advice, and a lesson direly in need of learning both as a child and an adult. Atticus is trying to teach the children that others deserve respect regardless of the inevitable rumor mill, which correlates with Atticus' defense of Tom Robinson throughout the novel. When Atticus warns the children not to kill a mockingbird with their new rifles, the mockingbird is symbolic of both Boo Radley and Tom.
Often times children, albeit innocent, create cruelty nonetheless. They do not take into account others' feelings of hurt or rejection. Atticus enforces this lesson by saying all people deserve dignity and privacy. It is a lesson for all humanity, as no one should directly inflict emotional pain onto others, especially for the sole purpose of entertainment.