What was the conversation atticus has with his brother jack in chapter 9 about how to answer a child's question.?

The conversation of Atticus and Uncle Jack revolves round Uncle Jack's admission that he will never get married and how he never understood children. Atticus tells him about the pros and cons of educating a child, the need to be truthful despite the circumstances which will only lead to the child learning about the reality of life.

Explanation:

Chapter 9 of Harper Lee's "To Kill A Mockingbird" revolves round the Christmas scene of the Finches where the whole family including Uncle Jack had gone to visit Aunt Alexandria and Francis. It was also the scene where Scout fought with Francis for calling Atticus a "ni__er-lover", which resulted in the scolding of Scout by Uncle Jack.

Later that night, when Uncle Jack and Atticus were discussing about the events of the day and Scout's impact on him, Atticus simply states that "When a child asks you something, answer him, Children are children, but they can spot an evasion quicker than  adults, and evasion simply muddles ‘em". This suggests that Atticus believes in putting the reality to a child's answers, instead of shrouding it with some lies. It s better for children to learn and adapt to things soon, rather than being shielded from the reality of the world.