What observations are you able to make about Atticus? What does the fact that Jem and Scout refer to him by his first name suggest to you about him?
Atticus in Harper Lee's To Kill a Mockingbird is an enigmatic figure and one of the great literary characters of American literature. One of his distinguishing characteristics is his principled set of morals, and his determination to be the same man in public as he is at home. In essence, Atticus aims to live authentically whether he is in private or amongst the community, and this means that he abides by his own moral code and does not bow to outside pressure. It is this characteristic that enables Atticus to rebel against the racist tendencies of his neighbors and defend Tom Robinson in court.
Atticus is also committed to education, and especially to educating his children. It's clear that he's instilled a love for reading and knowledge in Jem and Scout, and in doing so he has encouraged them to think of themselves as mature and intelligent individuals. As such, it makes sense that Atticus' children would refer to him by his first name. Rather than thinking of themselves as inferior to their father, Scout and Jem imagine themselves to be intellectually equal to him, and so they call him by his first name. All in all, the fact that Scout and Jem call Atticus by his first name reveals Atticus' determination to empower his children.
Atticus was a man who was generous with his money. He sacrificed some of his salary when he was a young lawyer to help pay for his brother's education at medical school. When one of his clients could not afford to pay him, Atticus accepted whatever they could give as payment. Mr. Cunningham could not afford to pay Atticus, so he left "a load of stovewood," "a sack of hickory nuts," "a crokersack full of turnip greens," and other things. This showed that Atticus was an understanding and compassionate man.
Scout and Jem called their father by his first name. This showed that he treated them more as equals than as children. He gave them a good amount of independence, and he encouraged them to do many things on their own. When Scout started school, Atticus had Jem bring her to her classroom, which was "a job usually done by one’s parents." Scout described Atticus as treating her and Jem "with courteous detachment."