Can all you people calling yourselves "street photographers" please stop whining every time someone on the street is annoyed by your annoying behaviour? If you seriously find it artistic to invade the privacy of complete strangers, at least have the decency to recognize they might get pissed off, particularly if someone tries repeatedly to get a picture of a child. It astounds me OP was so shocked by the mother's reaction. She doesn't know he isn't a pervert and is actually a street photographer (whatever that is anyway). And that doesn't even matter. Some people just plain don't like having their picture taken for no reason. I'm one of them.
No, a Leica doesn't make you any more legitimate. No, the legalities of the matter don't make your behaviour less creepy. And no, not everyone who objects to the way you make your "art" is mentally ill. OP is lucky all he got was a verbal reaction.