Cannot pair child Apple Watch to parent Apple ID

I (mom) bought an Apple Watch with cellular for my 8yo son to use while skiing. He has an Apple ID already. When I attempt to pair his new watch to my phone, I can start the pairing process but when it gets to the step of entering his Apple ID, the process stalls (spinning circle on the continue button), does this for 11 minutes, then automatically unpairs the watch. I have been to the Apple Store, reached out to support for hours, but nobody has been able fix this, they only say it is an issue with my Apple ID. Anybody have any advice? I’m desperate