I suspect Fall detection is only practical for the Family Setup scheme using Apple Watch with cellular. Without cellular the watch can't make the emergency call unless it has a paired iPhone, in which cased Family Setup is pretty much irrelevant! The problem with WiFi calling is that it doesn't give a useful location if the faller is incapacitated and unable to speak.
With the cellular version:
From the Family Setup guide Set up Apple Watch for a family member - Apple Support
Availability of features and apps
Health and fitness features:
- ....
- Fall Detection is available for users 18 and older.
- ....