"What's celebrity sex, Dad?" It was my 7-year-old son, who had been looking over my shoulder at my computer screen. He mispronounced "celebrity" but spoke the word "sex" as if he had been using it all his life. "Celebrity six," I said, abruptly closing my AOL screen. "It's a game famous people play in teams of three," I said, as I ushered him out of my office and downstairs into what I assumed was the safety of the living room.

No such luck. His 3-year-old sister had gotten...