Harper Lee and Mark Twain use Jean Louise (Scout) Finch and Huckleberry Finn as catalysts of innocence to prove that in extreme circumstances children can grow up exceptionally fast in their novels, To Kill a Mockingbird and The Adventures of Huckleberry Finn. Their young age and inexperience with the evils of the world leaves them impressionable and vulnerable. Scout and Huckleberry lack significant explanations of certain aspects of society and are forced to come to their own realizations, ultimately making them mature at a young age.
In To Kill a Mockingbird, Lee uses Scout to explain society's outlook on African Americans at the time. Although she is a child who has a black housekeeper, she doesn't really know of the prejudice that still lingers against them. Even though almost everyone in her neighborhood has such kind of help, the citizens of Maycomb still look and talk down upon the African Americans that live across town. Through her father's trial with Tom Robinson, Scout learns, along with Jem, that what society deems appropriate isn't always correct. Even though Scout had her doubts about Tom Robinson's charges being dropped at all, she was still crushed by the fact that the entire jury would vote against him. The whole incident makes Scout stop and consider things from Jem's perspective, who was having a horrible time after the trial because he understood what happened but didn't understand why. Having her brother drift away from her and become more mature leads Scout to tag along.
Huckleberry Finn had a similar experience, only at times, it seemed as if the roles were reversed. Tom Sawyer can be seen as "Jem" in Huck's life: the older, more learned, best friend but practically a brother. Except that Tom's learnedness gets the better of his romantic side and leads him to be rather childish at times. Where Huck can't understand his imagination, he sees things as they really were, showing his take-things-as-you-see-them attitude and level-headedness.