I have heard these answers seriously proposed:
1) smartphones and social mediaI find it hard to credit 2) and 3) for historical reasons: nobody noticed a big surge in youth anxiety in the Depression, and I find it hard to believe that Trump is more anxiety provoking than the Cuban Missile Crisis and nuclear attack drills. I acknowledge that racism, sexism, and other isms are still serious problems but I do not believe that they have gotten worse. Bad things cannot explain a doubling or tripling or more of the incidence of severe anxiety; only things that have gotten worse in the past 30 years can be possible explanations. The same goes for bullying; I am sure bullying is a major cause of anxiety in children but I do not think it has gotten worse, so it can't explain the striking increase.
2) economic stagnation leading to stress about success
3) political turmoil
4) over-involved parenting, excessively scheduled lives, etc.
5) too much emphasis on safety, not enough tolerance of risk in children's lives
6) living cut of from nature; not enough time outside, to much tv and digital media, etc.
I give some credit to our whole society's focus on risk. From where I sit on my train I can see five separate yellow and black CAUTION or EMERGENCY signs: for steps, a low bit of the ceiling, the emergency exits, the ax kept behind glass, and the instructions for what to do in an emergency. Everywhere you go on construction sites, loading docks, and other sites of manual labor you see signs that say SAFETY FIRST. All this focus safety has in fact made us safer; vehicle accident rates and on-the-job deaths are way down. But if you are really putting safety first all the time, could that make you anxious? Is the price of constant vigilance about dangers that we internalize the vigilance even when there are no dangers? Does a world full of yellow and black CAUTION signs promote a generalized anxiety?
I am also interested in the very safe way most of us live. Do children who are not allowed to wander the neighborhood, explore in the woods or build fires miss acquiring a resilience that more free-ranging children used to get? Which I'm not blaming just on cautious parents; in my experience children with the internet, video games and 500 tv channels are less interested in going out and exploring even when their parents push them to. But it seems to me that contemporary children get a lot less exposure to small doses of risk like bike-riding and tree climbing, and maybe that has long-term effects.
I don't know about pressure to succeed. I suppose it could be that some children are anxious because their parents push them too hard and sign them up for too may activities and talk all the time about getting into college. But I am skeptical that this can be the whole cause because I know anxious children of very laid-back parents. One of the teachers Denizet-Lewis spoke to said that some kids are driven to achieve by their parents but others do all the driving themselves, and this is also my experience.
Which leaves me wondering a lot about digital life. All the young people I know live largely in a digital world: television, music, video games, memes and Facebook make up a huge part of their lives, maybe the biggest part. I really don't know why that would promote anxiety; I am unimpressed by all the talk of how Facebook makes people hyper-self-conscious because I know anxious young people who are not at all into social media, and hyper-self-consciousness was a huge part of modern adolescence before computers came along. But when I look for a difference between how I grew up and how my children have, the digital world is the most salient thing I see. So by process of elimination I keep ending up thinking that too much digital life may be doing something bad to our brains.