“‘Once upon a time,’ said Frog, ‘there were two good friends, a frog and a toad.’” So says Frog in a story from “Frog and Toad Are Friends,” the first in the series of children’s books that chronicles ...

What makes a great love story? Maybe it’s chemistry, or devotion, or music swelling at the right moment. Or maybe it’s writing a letter just so the other person has a reason to check the mail. At ...