Consider this fair warning: If you’re going to bring your children around me, I’m going to teach them how to shake hands. The process, which I picked up from my dad, involves three simple steps: “firm grip, squeeze, look me in the eye.” When my father started doing this in the 1970s, the hardest step for many children was the first. This was the era when the demure four-finger handshake was still popular among women and girls. More recently, as gender equality has leveled the handshake, I’ve noticed that young people have an almost universal aversion to the final step.

No one will look me in the eye.

For a long time, I didn’t think much of this quirk. Children are often awkward around adults. Give them a few years and they’ll grow out of it, right?

Maybe not. A few years ago, I was having drinks one night with Clifford Nass, a restlessly creative communication professor at Stanford University who had a reputation for out-of-the box thinking. Dr. Nass told me about research he was doing that suggested young people were spending so much time looking into screens that they were losing the ability to read nonverbal communications and learn other skills necessary for one-on-one interactions. As a dorm supervisor, he connected this development with a host of popular trends among young people, from increased social anxiety to group dating.

I was fascinated but let the thread slide, and a few months later, Dr. Nass died suddenly on a hiking trip. In the intervening years, I’ve heard increasing alarm about the impact of technology on children. Was Dr. Nass right? I decided to revisit the debate to see what parents should know.