The word “scrotum” does not often appear in polite conversation. Or children’s literature, for that matter. Yet there it is on the first page of “The Higher Power of Lucky,” by Susan Patron, this year’s winner of the Newbery Medal, the most prestigious award in children’s literature. The book’s heroine, a scrappy 10-year-old orphan named Lucky Trimble, hears the word through a hole in a wall when another character says he saw a rattlesnake bite his dog, Roy, on the scrotum. “Scrotum sounded to Lucky like something green that comes up when you have the flu and cough too much,”...