A couple of years after smartphones became popular, my friend Joyce told me a story I found troubling. She had recently been on a city bus, sitting in an aisle seat. Directly across the way, an infant sat on a woman’s lap. Soon, the child looked Joyce straight in the eye and they started interacting — making faces at each other, smiling, shaking their heads, laughing. Then, in an instant, the scene changed. The caregiver pulled an iPhone from her bag and gave it to the child.