iPhone X owners can't use Face ID to approve family purchases

Face ID on the iPhone X is helpful for authorizing a purchase for yourself, but don't expect to use it if you're approving a purchase for your kids. Numerous owners have discovered that the face authentication feature doesn't work for family purchases (that is, where a family member asks you to buy apps or music on their behalf) like Touch ID does on earlier iPhones. It's not a tremendous pain, but you probably won't relish the thought of punching in your password every time your little ones want a new game for their iPads. We've asked Apple if it can elaborate on why Face ID doesn't work in these situations. Is it a security decision, a lack of time to add the feature or something else?