More than 100 child health advocates, medical experts, and civil society groups are urging Facebook to discontinue Messenger Kids, suggesting that it poses a danger to children and undermines their healthy development.

In an open letter led by the Campaign for Commercial-Free Childhood, the signatories say that “younger children are simply not ready to have social media accounts.” In particular, they point to the fact that these children “are not old enough to navigate the complexities of online relationships” and argue that social media use can affect kids’ mental wellbeing.

Those who signed the letter worry that Messenger Kids will only serve to increase the amount of time that young children spend on digital devices and believe that it is better to let children “develop without the pressures that come with social media use.”

They conclude: “Please make a strong statement that Facebook is committed to the wellbeing of children and society by pulling the plug on Messenger Kids.”

Facebook, for its part, has claimed that Messenger Kids was developed with input from online safety experts and includes strict parent controls and safety filters to ensure that children don’t share inappropriate content.

In a statement to Fortune, a Facebook spokesperson reiterated that the app was created “with an advisory committee of parenting and developmental experts” and said the company continues “to be focused on making Messenger Kids be the best experience it can be for families

The pushback against Facebook comes amid wider scrutiny of technology’s effect on the youth. Earlier this month, two of Apple’s major shareholders urged the tech giant to study iPhone addiction among kids.

“There is a developing consensus around the world including Silicon Valley that the potential long-term consequences of new technologies need to be factored in at the outset, and no company can outsource that responsibility,” they said.

This story has been updated with Facebook’s statement.