The actual quote you are referencing, I believe, is: "They’ve done it before and they did it tonight and they’ll do it again and when they do it – seems that only children weep?” This happens in Chapter 22 after the verdict in the courtroom. Atticus says it because no adult in that courtroom sheds a tear one way or another. That is because they have become desensitized to the racism that surrounds them...but the children haven't...and they cry.
