Why do you require a cellular phone to have a cellular watch? It’s forcing me to have 2 phone numbers for my 11 yr old just to have his cellular watch paired with his non-cellular iPhone

Either you use Apple Watch Family Plan, with all its limitations, or you pair the Apple Watch with an iPhone and share the iPhone's phone number.

if the iPhone does not have a phone number, then you cannot have a phone number on the Apple Watch.

That is how Apple designed it. There is no workaround.

You can send Apple feedback via: https://www.apple.com/feedback/watch If enough users send feedback, it is more likely a decision maker will see it, and maybe take action.

Am individual watch can be set up using a different device through family sharing. Otherwise, the watch is an extension of the iPhone. There is no WiFi only iPhone. Do you mean that he has no service on the iPhone? That would be a good first step. Many people have a cellular watch to use when not carrying their phone.