Ran Barzilay, a psychiatrist and researcher at Children’s Hospital of Philadelphia, won’t be letting his nine-year-old son get a smartphone before age 13. He made the decision based on data from his recent study, published in the medical journal Pediatrics, which linked getting a smartphone at a young age to worse health consequences. Kids who owned a smartphone by age 12 had a greater risk of depression, obesity, and insufficient sleep compared to those who didn’t, a research team led by Barzilay found. That was based on observational data collected between 2016 and 2022 in an ongoing study of more than 10,000 children across the United States. Designed to assess brain development and child health, the nationwide Adolescent Brain Cognitive Development Study has been following children for the last decade, starting from ages nine to 10 into early adulthood. The age at which kids got a phone in this cohort ranged from four to 13, with a median age of 11. “We’re not advocating for people to go back to the Stone...