When a pair of hand-me-down flip-flops recently arrived in the mail, my 4-year-old son gleefully announced they had Spider-Man, Superman, Iron Man, and Captain America on them. I looked at him quizzically. How did he know the names of these characters—some I didn’t even know? We haven’t watched their movies, read their books, or purchased their toys. When I asked him where he learned about these superheroes, he shrugged and said, “Everybody knows about these guys, Mama!”