What does atticus mean when he says, it 'seems that only children weep"?

When Atticus says these words, he means that nobody cares about the unfairness that undergoes the whole town, except the children that felt completely desperate because of all that was happening right before their eyes. Children were the only ones who weep at injustice because they are still capable of feeling outrage at unfairness unlike the adults who were neglectful.