How about The Hardy Boys? I read dozens of these as a young kid, and the thing that stands out in mind now is, there was always an answer to the mystery, one that could be arrived at via clues and deduction. Looking back now, I think they had a major impact on my manner of thinking, reading them as young as I did (kindergarten and 1st grade, I'm talking) such that years later I was inclined to look favorably upon a 'rationality technique' when I encountered the idea of one on OB.