DO YOU know any children? I’ll bet you’ve not had much eye contact with them recently, because they’re glued to their devices.

Ofcom reports that even three-to-four-year-olds now spend almost eight-and-a-half hours a week on­­line. For 12-to-15-year-olds it’s more than 20 hours, and three-quarters of them manage time-consuming social-media profiles on their smartphones.

The Education Policy Institute reports that more than one third of British 15-year-olds are now “ex­­treme internet users”, who spend at least six hours a day online; so the Children’s Commissioner has just launched a campaign to draw atten­tion to the nation’s digital obesity problem.

Entirely coincidentally, of course, one in ten children in the UK cur­rently suffers from mental-health problems. One of the ways in which we treat anxiety and depression is with drugs that increase your levels of serotonin, the chemical mes­senger in your brain which contrib­utes to your feelings of well-being and happiness.

In a famous study about vervet monkeys, the scientists Michael Mc­Guire and Michael Raleigh from UCLA found that the top-ranking monkeys in a troop had double the amount of serotonin in their blood than the next monkey down the hierarchy. If they were challenged by a junior monkey and lost their status, their serotonin levels plum­meted. They recovered only if their status recovered. The researchers found that the only other way to crash sero­tonin was to maroon a senior mon­key with only a mirror for company.

This puts me in mind of social media. Facebook is like a mega-troop of vervet monkeys, giving you instant and repeated feedback about your status in your social group. If you don’t get affirmation, you suffer the same fate as the monkey with the mirror, and start feeling depressed and anxious about your status.

But what if the nation’s declining mental health could be arrested if we were Facebook for each other, real-time? If we all had our affirmation needs met by people around us, would we feel the same draw to the online world?

Maybe it should be our mission to let no good act go unnoticed. Per­haps next time anyone is routinely nice to you, or wears a cheering out­fit, or is kind to someone in your presence, you could do the equiva­lent of Liking them. Not with an elec­tronic tick, but with a real in-person smile and some gentle praise.

Tertullian imagined that people would say of Christians “See how they love one another!” Maybe those children would look up if we gave them more reason to do so.

Dr Eve Poole’s book Leadersmithing is published by Bloomsbury. Angela Tilby is on holiday.