The twentieth century was, by any reckoning, the age of the child in America. Today, we pay homage at the altar of childhood, heaping endless goods on the young, reveling in memories of a more innocent time, and finding solace in the softly backlit memories of our earliest years. We are, the proclamation goes, just big kids at heart. And, accordingly, we delight in prolonging and inflating the childhood experiences of our offspring. In images of the...