When I was a kid in the 1980s, my parents sent me to a Waldorf school in England. At the time, the school discouraged parents from allowing their kids to watch too much TV, instead telling them to emphasize reading, hands-on learning and outdoor play. I chafed at the stricture then. But perhaps they were on to something: Today I don’t watch much TV and I still read a lot. Since my school days, however, a far more insidious and enticing form of tech has taken hold: the internet, especially via smartphones. These days I know I have to put...