The debate over how much time children should spend on digital devices like smartphones is raging on. Following its introduction last month, child health experts and groups are urging Facebook to kill off its Messenger Kids app.

Over 100 child health advocates, medical experts, and civil society groups have signed an open letter addressed to Facebook CEO Mark Zuckerberg urging him to discontinue the standalone Messenger app aimed at children under 13, who aren’t allowed a Facebook account.

While Messenger Kids is managed through a parent’s Facebook account, letting them choose and approve who their children communicate with, the signatories say young users are “are not old enough to navigate the complexities of online relationships, which often lead to misunderstandings and conflicts even among more mature users. They also do not have a fully developed understanding of privacy, including what’s appropriate to share with others and who has access to their conversations, pictures, and videos.”

Additionally, it’s argued that the app will cause children to spend more time using digital devices, which researchers say can stunt development skills. The letter also cites studies that show links between social media use and depression, and how adolescents who spend an hour a day chatting on social networks report less satisfaction with virtually every aspect of their lives.

The letter adds that while it understands some conversations can’t be face-to-face, such as speaking to long-distance family members, including parents in the military, it suggests using Skype, a parent’s Facebook, or other accounts in these situations.

“Messenger Kids is not responding to a need – it is creating one,” claims the letter.

In response, Facebook's global head of safety, Antigone Davis, said in a statement to the Washington Post, "We worked to create Messenger Kids with an advisory committee of parenting and developmental experts, as well as with families themselves and in partnership with National PTA. We continue to be focused on making Messenger Kids the best experience it can be for families."

Earlier this month, two Apple shareholders urged the company to address the issue of mobile device use among children and investigate the effect it can have on their mental health.