Ah, to be young, free, and careless. (Actually, we still are, and it's awesome.)
In From the Mixed-Up Files of Mrs. Basil E. Frankweiler, Claudia and Jamie are young and free, at least—though not careless. They're pretty careful, in fact, for a couple of kids. The book deals with two kids who are taking on very adult situations, and how that plays out. They find a place to live and provide for themselves, they learn how to budget, and they even take on a bona fide academic research project. At the end of the day though, they're still a couple of kids, albeit pretty smart and quick-witted ones.
Even though running away is a textbook childhood activity, once Claudia and Jamie do so, they start taking on more and more adult responsibilities.
Claudia and Jamie may be young, but they've managed to achieve a lot more than most adults.