What does Atticus mean when he says, "this is their home, sister. We’ve made it this way for them, they might as well learn to cope with it” (243)?

In chapter 22, Atticus and his children return home following the Tom Robinson trial and Jem is visibly upset. When Aunt Alexandra sees him, she tells Atticus that she doesn't think it was wise to allow the children to watch the trial. Atticus responds by telling Alexandra,

"This is their home, sister . . . We’ve made it this way for them, they might as well learn to cope with it." (Lee, 216)

Atticus is essentially telling his sister that sooner or later Jem and Scout were going to have to learn that they live in a racist community that discriminates and marginalizes black people. Atticus is an honest parent and does not plan on shielding his children from the harsh realities of life. He believes that it is better to expose his children to racial injustice rather than protect them from the truth about their "Christian" town. Atticus views the Tom Robinson trial and its unfortunate outcome as a learning experience for both of his children and an opportunity for them to understand the effects of racial prejudice. While Atticus knows that witnessing Tom's wrongful conviction is traumatizing for Jem, he also understands that it is necessary that his son realizes the risk he took defending Tom in front of a prejudiced community.

Atticus addresses these words to Aunt Alexandra not long after the trial of Tom Robinson. She has scolded Atticus for allowing his children to attend the trial. As far as she is concerned, Scout and Jem are still innocent in the ways of the world and so need to be protected from harsh, unpleasant truths. But Atticus is much more practical and realistic than his sister. He knows that at some point the children are going to have to have their eyes opened to what life in Maycomb is really like, with all its unfairness and cruelty. The people of Maycomb have created a world in which the terrible injustice done to Tom Robinson is the norm. The culture that gave rise to Tom's conviction cannot be changed overnight. In the meantime, the Finch children need to live in the world bequeathed to them by the adults of Maycomb. And to do this they need to know the truth instead of being kept in a state of innocence.