Like a crisp breeze through the election year’s hot rhetorical winds comes “Son,” Lois Lowry’s beautifully wrought political fable that concludes the series she began in “The Giver.” Called “remarkable” and “unforgettable” in a Washington Post review two decades ago, “The Giver” won a Newbery Medal in 1994 and become a classroom staple, the kind of book sure to spark lively discussion.