A child climbs a jungle gym at Spark Park in Leesburg, Virginia, on December 19. Photo / Maxine Wallace, The Washington Post
University of Pennsylvania researcher Ran Barzilay is a father-of-three.
His first two children received cellphones before they turned 12.
This year as early results from his own study on screens and teen health rolled in, he changed course.
His youngest? Not getting one anytime soon.
Barzilay’s analysis of more than 10,500 children across 21 United States sites found that those who received phones at age 12, compared with age 13, had a more than 60% higher risk of poor sleep and a more than 40% higher risk of obesity.
“This is not something you can ignore for sure,” said Barzilay, a professor of psychiatry and a child-adolescent psychiatrist at the Children’s Hospital of Philadelphia.
For years, the debate over teens and screens has been defined by uncertainty.
Parents, teachers, doctors and policymakers have argued over whether phones and social media were truly harming young people, but the evidence has often been thin, anecdotal or contradictory.
That picture shifted dramatically in the second half of 2025.
A wave of large-scale studies is quantifying how early smartphone access and heavy screen use can harm adolescent minds - and the findings are aligning in a way earlier research rarely did.
The numbers suggest screens are taking a broader, deeper toll on teens than many expected.
The debate is shifting from one about whether screens have an impact - to one about how far-reaching that impact might be and what society is willing to do about it.
Australia this month became the first country in the world to ban social media for children younger than 16. The companies running TikTok, YouTube, Instagram and Facebook were ordered to block access starting from December 10.
Malaysian officials said a similar ban is starting in 2026, and the move is being watched by other countries that are considering adopting their own measures.
Since Steve Jobs marched onto a stage in San Francisco in his trademark black turtleneck and unveiled the first iPhone in 2007, arguments over what smartphones are doing to us - especially to children - have relied heavily on anecdotes.
Teachers blame slipping grades on TikTok distractions; parents worry about video game binges; clinicians point to online bullying and rising rates of adolescent self-harm.
Yet for all the cultural heat around screens, the science has been slower to coalesce.
Part of the difficulty is methodological. Researchers can’t evaluate phones the way they might test a drug, in a controlled trial with clear exposures and outcomes.
Most studies of teens and screens are observational, sifting through large datasets to detect associations between digital habits and health. These studies can’t prove causation. But they can, over time, illuminate patterns strong enough to be hard to ignore.
For years, even these efforts were limited by data: small samples, short follow-ups, uneven measures of screen behaviour.
That began to change over the past few years with the release of data from the Adolescent Brain and Cognitive Development study, a National Institutes of Health initiative tracking almost 12,000 children born between 2005 and 2009.
As the ABCD cohort ages, researchers are gaining an unprecedented longitudinal window into how today’s teens are developing - and how technology might be shaping them.
One striking paper, published in June in JAMA and using that dataset, distinguished between sheer screen time and what it called addictive use. The difference proved consequential.
Total hours online did not predict suicide risk. But compulsive patterns - distress when separated from a device, difficulty cutting back - did. Teens whose addictive use increased over time had two to three times the risk of suicidal ideation and behaviours compared with those whose use remained low.
Their work also found differences in the type of online activity and risk.
Children who had high and increased use of video games had more internalised mental health challenges such as anxiety and depression, while those with high and increasing social media use tended to have more externalising behaviours such as rule-breaking and aggression.
Yunyu Xiao, a professor of population health sciences at Weill Cornell Medicine, said the results suggest that there are groups more susceptible to suicidal ideation and behaviours related to online platforms and that more work needs to be done to figure out what makes one child more vulnerable than another.
“If kids come into a clinic at age 10, we want to be able to know who is at risk,” Xiao said.
This December brought a wave of new analyses from the ABCD data, each probing a different facet of adolescent health.
A research letter in JAMA examined social media use and cognitive performance in children aged 9 to 13.
The authors identified three trajectories - little to no use, low but increasing use, and high and increasing use.
Children in the latter two groups showed slightly poorer performance across a range of cognitive tasks, including oral reading recognition, picture-sequence memory and vocabulary tests. The differences were modest, but consistent.
The authors noted that social media might displace activities more directly tied to learning - an idea echoed in earlier work.
Lead author Jason Nagata, a professor of paediatrics in the division of adolescent and young adult medicine at the University of California at San Francisco, said that while the differences accounted for only a few points on some tests, they can be thought of as similar to a teen’s grade going from an A to a B.
“What was surprising to me was even the low users - those with an hour of social media a day - had worse cognitive performance over time than those with no social media,” Nagata said.
Another study, posted as a prepublication in Paediatrics, examined attention and found that social media use - unlike gaming or watching shows - was linked to increased symptoms of inattention.
“Social media provides constant distractions,” said Torkel Klingberg, a co-author of the study and a cognitive neuroscience professor at Sweden’s Karolinska Institutet.
“If it’s not the messages themselves, it’s the thought of whether you have a new one.”
Klingberg noted that the findings align with the idea that cognitive abilities are malleable.
“It depends on whether you’re training them or not,” he said. “If you’re constantly distracted, your ability to focus may gradually become impaired.”
A fourth analysis, led by Barzilay and published online on December 1 in Paediatrics, explored whether the age at which US children receive their first smartphones influences later wellbeing.
Its conclusions resonate with a large international study published in July in the Journal of Human Development and Capabilities, which found that receiving a smartphone before age 13 “is associated with poorer mind health outcomes in young adulthood, particularly among women, including suicidal thoughts, detachment from reality, poorer emotional regulation, and diminished self-worth”.
Barzilay stresses that he and his co-authors “are not against technology”.
It offers many benefits, he said, but parents should take the decision of when to give a child a smartphone seriously.
Morgan Cobuzzi first encountered the movement to delay children’s access to smartphones the way many parents do now: on Instagram.
Cobuzzi, 40, a former English teacher in Leesburg, Virginia, and a mother-of-three, was already uneasy as her oldest daughter approached age 10, with intermediate school only a year away.
She worried less about the device itself than about what came with it - the anxiety teenage girls absorb from social media feeds built on impossible standards.
About half of her daughter’s classmates have phones, Cobuzzi estimates, and almost all have access to iPads, a dynamic that can leave screen-free children feeling socially excluded.
Still, she has watched a quiet counterculture emerge. On snow days and other school-free afternoons, children have been rotating between houses, playing outside and baking - passing the time offline.
In October, Cobuzzi launched a local chapter of the Balance Project, a national group focused on helping families find a healthier relationship between digital life and the real world.
About 40 families have contacted her since. What once might have seemed fringe, Cobuzzi said, is increasingly common - especially among millennials like herself unsettled by how different their children’s childhoods look from their own.
“Ten years ago we didn’t realise the negative effects of smartphones. Now we do,” she said.
Jennifer Katzenstein, a paediatric neuropsychologist at the Johns Hopkins University School of Medicine, said the most effective way for parents to manage teens’ screen use is not through bans, but through example.
Children closely mirror their parents’ habits, she noted, particularly around night-time phone use and sleep.
Research suggests that gradual reductions - cutting daily screen time by even an hour - are more effective, and more sustainable, than going cold turkey, leading to better long-term wellbeing and quality of life.
“The research suggests that just decreasing our device use by one hour per day has better long-term impact and decreasing overall device use results in higher quality of life than trying to go cold turkey,” Katzenstein said.
Megan Moreno, co-medical-director of the Centre of Excellence on Social Media and Youth Mental Health at the American Academy of Paediatrics, said smartphone use is not a one-size-fits-all approach when it comes to outlining guidelines and rules for preteens and teens.
“A huge piece of this is having early and ongoing communication, because one of the things that we hear from teens is that adults in their lives are often very reactive to their phone use.”
In the wake of the recent studies, Barzilay said, friends and relatives around the world have been asking him for guidance.
His two older children, now 18 and 14, received phones before they turned 12. But he recently explained to his 9-year-old why he will not be getting one yet.
“This is to keep you healthy,” Barzilay recalled telling his son. “You have your whole life to use smartphones and technology. We want to introduce them in a responsible way that supports your wellbeing.”
He emphasised that parents shouldn’t feel guilty about giving their children phones.
“It’s very important to me that this isn’t about blaming parents,” he said.
“Kids got smartphones at very young ages in the past because we didn’t know. Now we know.”
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