Face ID not available

Several months ago we got my 12 year old daughter an iPhone XR. She is setup with a child AppleID and we use family sharing and screen time controls.

She recently advised that Face ID does not work in her phone. I recently corrected her age on AppleID so that we could leverage the features of Screen Time. If she tries to reset FaceID and set it up, she continues to get the message “Face ID not available”. What does this message mean? I’ve gone through the whole FaceID troubleshooting guide in the Apple support page (including phone restore!) but nothing works.

The only remaining possibility is that there may be an age requirement/limitation for Face ID? I’ve found some articles online that indicate this might be the case but nothing clear in any Apple documentation. Please confirm if this is “by design” . Otherwise do I need to investigate a hardware issue with the front sensors?

Thanks.