Atticus gave his children air rifles for Christmas, but he told them never to point them at anyone and to never shoot a mockingbird.
Atticus does not like guns much. He is a crack shot, but when he kills the rabid dog he says he hasn’t shot a gun in 30 years. He does not want to give his children rifles and tells them that if they make “one false move he'd take them away from us for good” (ch 9). Atticus has only given in, buying them guns.
Atticus tells Jem that he can shoot at all the bluejays he wants, but “it’s a sin to kill a mockingbird" (ch 10). Scout comments that her father has never said anything else was a sin before, so she asks Miss Maudie what he meant.
"Mockingbirds don't do one thing but make music for us to enjoy. They don't eat up people's gardens, don't nest in corncribs, they don't do one thing but sing their hearts out for us.” (ch 10)
Atticus has taught his children a valuable lesson. You don’t target creatures that aren’t doing any harm. In the book, this is significant because there are several symbolic mockingbirds. Boo Radley is one of the mockingbirds, because he is a victim of society but never has hurt anyone. The other mockingbird is Tom Robinson, who is also victimized by society in a different way. Boo is the victim of society’s expectations, and Tom is the victim of society’s prejudices.