“People think The Magic Flute is the kind of opera they ought to schlep their children to,” Maurice Sendak told The Washington Post back in the 1980s, “and they’re not wrong. But what I love most about it is its seriousness of purpose. It is about enlightenment.” Sendak loved music, opera, and Mozart, and his beguiling sets and costumes for The Magic Flute are, well, magical. —L.J.