Facebook Messenger Kids is a messeging app designed, principally, for children age six and younger. The objective is to allow young children to communicate with family and friends in a completely secure environment. To that end, an adult must first open the account, and then app offers a variety of features to guarantee the security of the child.
Just like the normal Facebook messenger, with Facebook Messenger Kids you can send stickers, gifs, photos, etc. But this app also comes with filters and other tools to make it more fun for kids!
Facebook Messenger Kids is Facebook's attempt as creating a safe space for young children (age six and under) to easily send messages to their parents and close friends.