Children are starting on social media at an age that's younger than ever before -- and they're spending more time doing so. That's according to a new study by Common Sense, which reveals children as young as 8 years old are now commonly using social media. And many of them are spending as much as a third of each day online, according to the study. Time spent on social media for tweens -- a group comprising children between the ages of 8 and 12 -- climbed 17 percent between 2019 and 2021, researchers found. Moreover, 38 percent of all tweens now use social media, which is up a whopping 31 percent from 2019, the study reports.