On my wife’s birthday, I gave her a wrapped DVD—Titanic. Our three-year-old, Max, immediately asked, “Can I watch it after nursery?” I explained it was “for grown-ups only.” That day at school, he proudly announced to teachers and parents that “Mommy and Daddy watch Titanic alone at night.” Everyone laughed, but something lingered. Max became fascinated—not with the film, but...