jem and scout call their father by his first name what does this tell about their relationship

The children's relationship with their father goes beyond what most expect between a father and his children. Atticus is father, mother, mentor and friend. Atticus speaks to Jem and Scout like adults has always treated his children with the respect afforded to adults. He seldom keeps the truth from them, and there is hence a mutual, even adult, dialogue between them. The Finch Children have an uncommon bond with their father that is reflected in how they address him.