Look at all of the playful stuff they do. This is why I loved this book when I was a boy. They pretend to be pirates. They make wooden swords and have treasure maps. They do things they aren't supposed to do like smoking pipes and playing hooky from school. They just love to do stereotypical boy things. All of this kind of stuff made them seem like ordinary boys to me when I was young.
Mark Twain set Tom Sawyer and Huckleberry Finn up as foils to each other, but the boys do share enough in common to sustain the friendship. They love childish pranks, foul language and generally being silly; although Twain explores some serious themes in the novels, the overall tone is light-hearted and even humorous at times, as the boys engage in adventures based on Tom's obsession with and devotion to adventure and romance novels. Interestingly, although Tom is the one from a "respectable" family, while Huck is the uneducated son of an abusive alcoholic, it is Huck who quietly questions what he believes is wrong in society while Tom maintains a rigid, and at times absurd adherence to society's rules. Tom knows that Jim is free because Mrs. Watson has died, but he doesn't tell Jim; Huck, on the other hand, puts himself in danger by lying to slavehunters to protect Jim.