Yes, you can monitor your child’s disappearing messages on Facebook Messenger with a third-party parental control app. My favorite is mSpy. It has a social media monitor that tracks everything your child is sending and receives on Facebook Messenger, a keylogger that logs what your child types in the app, and a screen recorder that takes screenshots of your child’s activities in Messenger. This allows you great insight into your child’s conversations on Messenger, even when they use disappearing messages.