In general, Atticus believes in answering his children's questions honestly and correctly. The main example we see of this is when his daughter, Scout, asks him what rape is.
When she asks him this, remember, she is only in second grade. But he does not put her off or anything like that. Instead, he tells her explicitly what rape is.
To me, this is an indication of Atticus's overall character. In the story, he stands for truth and morality. His honesty when talking to his children is part of this image.
Atticus treats the children in many ways just like miniature adults. He does not sugar coat the world in which they live. Although he generally gives a positive spin on the way he presents people and relationships to the children, he tells them the truth about people and events.
Atticus has a strong sense of being a good and honest citizen in his role as a father. His words are a reflection of his actions. The man is true to his words.
As a father, he also tries to teach the children to look at both sides of issues. when Scout becomes upset with her teacher and later tells Atticus how she had cried in the classroom and had responded to her humiliation by Mr. Ewell, Atticus speaks to Scout about understanding how it takes time for one to adjust to new settings and people.
Words for Atticus are critical and not used lightly in his home. Therefore, when he answers his children's questions he contemplates his answers and gives them honest answers that are non-condescending.