Facebook's messaging app for children below 13, Messenger Kids, where kids can chat with other children approved by their parents was initially reported to have a design flaw that allow unapproved users including adults to join group chats of kids.
Children using Messenger Kids can only talk to each other with a parent or guardian's approval; however in group chats a child can come into contact with a third person who, while approved by one child's parent, is not approved by the other.
Facebook has stated that they have informed parents who use Messenger Kids about the error and turned off group chats. However, they have not confirmed how many chats were affected by the flaw for how long.