A coalition of 97 child health advocates sent a letter to Mark Zuckerberg on Tuesday asking him to discontinue Messenger Kids, a new advertising-free Facebook app targeted at 6-to-12-year olds.

Advocates say the app likely will undermine healthy childhood development for preschool and elementary-school-aged kids by increasing the amount of time they spend with digital devices.

The letter to Zuckerberg was signed by individuals and 19 nonprofits including Common Sense Media, Campaign for a Commercial-Free Childhood, and Parents Across America, who say their concern stems from recent studies that link increased depression, poor sleeping habits, and unhealthy body image in children and teens with higher use of social media and digital devices.

For instance, a study by Jean Twenge, a psychology professor at San Diego State University and author of iGen, found that social media use by teens is tied to significantly higher rates of depression.

Another recent study found that adolescents who spend an hour a day chatting on social media report less satisfaction with nearly every aspect of their lives and 8th graders who use social media for six to nine hours per week are 47 percent more likely to report they are unhappy than their peers who use social media less often.

“Raising children in our new digital age is difficult enough,” the letter says.

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