I have wifi calling on my iPhone 12pro but don’t have option to turn on wifi on other devices
You can also see the 'Make calls over Wi-Fi' section in:
Make phone calls on Apple Watch - Apple Support
but I believe this does not apply to a watch using Family Setup (which I assume is how you setup your child's watch).
As far as I know, Wi-FI calling is not supported on the watch except thru the paired iPhone.
About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support
Yes I saw this and contacted apple support but they said it only works if connected to my Apple ID and in that case the kids would receive my phone calls. They escalated as a concern but who knows if and when it will be available
Thanks you may be right. Seems to be a lot of confusion from both t-mobile and apple on this one.
You're welcome.
Why is child’s iwatch not linking to wifi calling
