I remember being shocked, in 1999, after setting up my hulking desktop and connecting my dial-up for the first time, to hear “You’ve got mail!” And I remember being even more shocked, in that first session, to receive an chat message asking what I was wearing—and if I could take it off.

When my now 18-year-old stepdaughter was four years old, I realized she was extremely mature for her age. Example: once, while we were watching a movie together, a couple retired to the bedroom with a look of come-and-get-it on their faces. It was subtle enough that I didn’t think a four-year-old would think anything…