Child Cant face time with family sharing

In the affected phone, Settings, FaceTime, turn it off.

Restart the phone.

Settings, FaceTime, turn it back on.

After that https://support.apple.com/en-us/HT204168

If you are using family sharing then can I also assume they have their own AppleID's?

If so then sign out of the phone and sign into it with the other child's ID.

If it still doesn't work then it

would seem to be hardware .

Can we assume each child has their own device?

Is there any difference in the way you set up their Screen Time?

The only age limit I am aware of is around 13 to have their own Apple ID (it varies)