And why Apple don't let people sync their Apple Watch with multiple iPhones?
For example a kid wearing an Apple Watch don't want to always wear his iphone to all places, or sometimes the kid could not haven even an iPhone, but use the father or mother iPhone to use his apple watch.
By letting people sync their apple watch with multiple iPhones suddenly Apple is opening the market for more people to buy an Apple Watch. You could limit the info you want to sync with a given iPhone, or let the Apple Watch use only some features like access to network.
Except that's not in Apple's best interest. You should buy one watch for each phone. ;-)
The good news is, then you can use whichever watch you want with whichever phone.
I fully expect once the watch is more autonomous (and it's darn close now), that Apple will allow people to pair with iPads, iPods (if they're still around), and Macs, which will also open up the market for new potential sales where there were none before (not everyone has an iPhone -- in fact most don't). Once that happens, then Apple may be open to allowing pairings among multiple devices. I can't see any reason why it wouldn't be possible, since there's not really anything stored on the watch anyway, and all the Apple devices will share the information anyway.
As to your example, it's kind of messy right now. What if dad and mom and Jr., all pair their watches to the same device? All the data would be confused. It seems to me that with Apple's move to offer multiple accounts on the iPad for education, they are planning a solution to eventually address this problem. I certainly wouldn't want to give my kid my iPhone without the ability for him to use his own account and not accidentally screw up anything on mine.
Right now, Apple is addressing the thing that brings them the most money and helps satisfy customer choice. Once they have an elegant solution for dealing with multiple device pairing, then they will implement that.
