Painted into a corner...

Let's start this off by reminding everybody that, as the good civil libertarians at a certain website proclaim in their very name, Photography Is Not A Crime.

And the folks at Photography Is Not A Crime (or PINAC) are on the same page with the cops and the courts on another basic issue:  If you are sitting in a place of public accommodation with two walls composed of floor-to-ceiling plate glass windows, you don't have much of a reasonable expectation of privacy, and therefore no real legal protection from being photographed.

And if the place of public accommodation you're in is staffed by people who just got a whole mandatory day of sensitivity training about their customer (and non-customer) service policies...

...how do you expect them to make someone stop taking pictures of your kid?

And why is this Starbuck's problem? Can you not ask the dude to stop yourself? And do you understand that, depending on jurisdiction, there might be no up-front legal reason he needs to? Now what?

(Personally? I'd leave. Simplest solution.)