Ebbie, I know what I would have done. I would have told that clueless mother to take her brat in hand or I would call the police. Animal cruelty is still illegal.
That incident on the plane...I can't imagine anything more like HELL than sitting near people like that! The last time I flew to the UK, there was a clueless mother a few seats ahead with a small child that howled most of the way over there.
None of my kids ever acted like savages at any age. And, I never had to smack them either.