Transferring Kids Apple Watch on Family Setup to First iPhone

You will need to unpair then repair your child’s Apple Watch to their new iPhone. No need to erase unless you planned to not set it up again. When unpairing you should be prompted to keep or erase the cellular plan, if you want to use the new iPhone number you’ll want to erase. Yes, the Apple Watch will be reachable at the new iPhone’s number is you transferred it. If you don’t have a cellular plan with the Apple Watch, the iPhone will need to be nearby to allow the Watch to make and receive calls. If you do have a cellular plan with the Apple Watch, it can make and receive calls on its own anywhere with the same number.

Note: You might see a phone number assigned to your Apple Watch that differs from the phone number assigned to your iPhone. The number shown for your Apple Watch is for your carrier's billing or tracking purposes only; your iPhone and Apple Watch share the same number.

mkirk76 wrote:

“When unpairing you should be prompted to keep or erase the cellular plan, if you want to use the new iPhone number you’ll want to erase.”

So, since we want to use the new iPhone number, we will need to erase - will we then be given an option to add a new cellular plan when pairing to his phone?

Yes, but you haven’t yet specified whether you want the Apple Watch to have a connection off the iPhone or its own cellular plan. If you want its own plan, you’ll tap add new. Otherwise no need.

mkirk76 wrote:

It’s own cellular plan so it can be used without the phone.

This seems like it doesn’t make much sense, though. Why do I have to erase the cellular plan it currently has just to add a new cellular plan?

Because the current plan he has is his old number and it would be a different number if he kept it once he paired the new iPhone. Also Apple Watch only allows one SIM at a time. By erasing then adding a new SIM, you can setup the new number for use.