To not know how to set up a smartwatch

[Imoapinn]

If I buy a smartwatch for my 11 year old, how do I pay for texts and calls on it?
Do they come with their own number?
I want my DC to be able to text and call from their watch. They don't have a mobile phone.
Can I buy one and link it to my mobile texts/calls?
Can someone explain in very simple terms - I'm a complete dinosaur!

You will need to get a sim card for it, you insert it as you would a phone.
Depending on the watch, some need an app some are stand alone.
My dc had a smart watch aimed at children whith phone capability without an app and it was much easier to use than DN's who had an app.
The only benefit of the one with the app was that it also had GPS on it.