Woah. His reaction to her speaking Korean to him the first time is surprising! And what a shock for her, too, to suddenly feel like she had alienated her baby. Ouch.

The linguistic development in children is a fascinating thing... I've known several multicultural children who were fluent in several languages by the time they started school.

I also had a girlfriend who had learned Czech when she was a child, and then got a job in Prague. And the first day at work she was mortified to learn that she had basically learned "baby talk" in Czech, and couldn't carry on a business conversation. She had to do a crash course in "adult Czech" to be able to do her job!

And for me... anytime anyone speaks to me in any foreign language, I immediately respond in Hungarian... the only foreign language I was ever any good at. That's a weird brain-thing; I hear a foreign language, so I automatically speak the only one I know... a small, niche tongue, that is rarely heard outside its home country, and has little use in the world.

At least I know the "formal" form, so I can speak to Hungarian grandmothers politely. Because THAT happens so often... not. :-D