You’ll finally be able to approve family purchases with Face ID in iOS update
In the iOS 11.3 beta, parents and other "family organizers" are now able to approve purchases through iOS' "Ask to Buy" feature using Face ID on the iPhone X. This addresses a prior complaint from users who upgraded from Touch ID iPhones to the iPhone X with Face ID.
Previously, iPhone X users had to manually enter their passwords via the iPhone X's keyboard to approve any request from a child to download an app or make an in-app purchase, whereas other iPhone owners could use Touch ID. It might not seem like a major inconvenience to some, but some parents with several children, all of whom have iOS devices and are playing games that involve frequent, small in-app purchases, went to Apple's forums to complain about the constant hassle.
Apple promoted Face ID as a complete replacement for Touch ID when the iPhone X launched. In fact, third-party apps that used Touch ID could authenticate with Face ID automatically, with no action required on the part of the developer in most cases. We found when reviewing the phone that Face ID could be used to make other kinds of purchases, so it was perplexing to users when this one feature—Ask to Buy—was not supported.