"Younger children are not old enough to navigate the complexities of online relationships,” the group wrote in the letter. "Children 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."
The company says the app, a standalone service that children as young as 6 years old can access through a parent’s Facebook account, was developed with along with parents and experts and is a safer environment for children.
"Messenger Kids is a messaging app that helps parents and children to chat in a safer way, with parents always in control of their child’s contacts and interactions," the company said in a statement to ABC News. "Since we launched in December we’ve heard from parents around the country that Messenger Kids has helped them stay in touch with their children and has enabled their children to video chat."
However, the group of experts who co-signed the letter believe that encouraging kids to take their friendships online will displace face-to-face interactions, which they say are essential for building healthy developmental and reading skills, as well as an ability to connect with human emotion and engage with the physical world.
A recent study released last week by San Diego University showed that increased use of smartphones and social media can cause a greater sense of unhappiness among teenagers. The research showed that children who spend more than two hours a day on their digital devices, had disproportionate feelings of unhappiness among compared to children who spent more time doing non-screen activities.
Facebook said that the app will not include traditional Facebook features such as News Feed and a "like" button, which mental health experts have linked to increased anxiety among adolescents. The company added that it had consulted with the National PTA, academics and several families before introducing the app.