In the novel To Kill a Mockingbird, why is Jem and Scout's perception of Atticus ironic?

At the beginning of Chapter 10, Scout laments her father's lack of talent and old age. She mentions that he is much older than her friends' parents, and he does nothing interesting. Scout and Jem both find their father to be boring and are ashamed of him. Scout says,

"Our father didn't do anything. He worked in an office, not a drugstore. Atticus did not drive a dump-truck for the county, he was not...

At the beginning of Chapter 10, Scout laments her father's lack of talent and old age. She mentions that he is much older than her friends' parents, and he does nothing interesting. Scout and Jem both find their father to be boring and are ashamed of him. Scout says,

"Our father didn't do anything. He worked in an office, not a drugstore. Atticus did not drive a dump-truck for the county, he was not the sheriff, he did not farm, work in a garage, or do anything that could possibly arouse the admiration of anyone." (Lee 118)

She even comments on that fact that he has to wear glasses, which is never cool in the eyes of a child. They even consult Miss Maudie and ask her if Atticus can do anything. She tells them that he can play a Jew's Harp and is the best checker-player around. The children are unimpressed and are still ashamed of their father.

Later on in the chapter, a rabid dog named Tim Johnson is walking down the main road of Maycomb. When Sheriff Tate arrives, he calls over to Atticus and gives him his gun. Atticus reluctantly takes Sheriff Tate's rifle and shoots Tim Johnson, killing him in one shot. The children are amazed at their father's marksmanship abilities. Miss Maudie tells them that she forgot that Atticus was the best shot in Maycomb County, and he had the nickname Ol' One Shot Finch as a young man. Jem and Scout are in awe, and Scout can't wait to go to school and brag about her father's marksmanship abilities.

Their perception of their father is ironic because they think he is talentless and boring at the beginning of the chapter, when in reality, Atticus is the most talented marksman in all of Maycomb County. In the eyes of a child, being the best shot in the entire county is probably the coolest, most interesting skill an adult can possess.