FaceTime audio calls not routed to Watch, but iMessage works

Hello, A child Apple ID is in to an iPad and to an Apple Watch. When I call the Apple ID on facetime audio, the iPad rings, but the Apple Watch does not. The Apple Watch is on the cellular network (not wifi). The iMessages to that same Apple ID do get routed to the Watch. I use the Apple ID (not phone number) to send the iMessage, so I know for sure that it is not an SMS but an iMessage.

The Apple Watch is set up in family setting (has its own phone number).

Please let me know how this issue can be resolved.