Apple: don't use Face ID on an iPhone X if you're under 13 or have a twin
https://www.theguardian.com/technology/2017/sep/27/apple-face-id-iphone-x-under-13-twin-facial-recognition-system-more-secure-touch-id
Facial recognition system is 20 times more secure than Touch ID, but struggles with young users and siblings
The iPhone X might be the future of Apple’s smartphone design, but its lauded Face ID facial recognition system has an issue with people under 13: it’s much more difficult to tell them apart.