Family sharing issues for apple watch

I have tried to set up an Apple Watch SE for my son with family sharing. We don’t want him having a phone just yet but the Apple Watch would tick all boxes. We bought an Apple Watch SE yesterday.

the phone will not allow us to pair with family sharing. We have paired the watch to my account and everything works without an issue.

we have set up his own account and everything works fine if we link the watch to that account on a test phone in the apple shop. It’s when we link the watch to my phone and family sharing. Phones are all

up to date, team in apple can’t find any issues and think it may be an issue with apple family sharing. Is anyone else experiencing this?