We're fast learning how smartphones impact childhood , and the findings of a new study about young tweens on the cusp of adolescence make for some more uncomfortable reading. Researchers in the US have found that owning a phone at the age of 12 was associated with an increased risk of depression , obesity, and insufficient sleep, compared to not having one. The iPhone launched less than 20 years ago, so for many kids now entering their teenage years, they've only ever known a world with phones.