- But that's the crux of the problem. - Not faulting you for your reaction but when you stooped down to her level she was able to follow you further with her dumb retorts and probably felt a 'REAL' conversation was going on.
I pity anyone put into the situation you were and I agree that calling those brats down was better than doing nothing but you put yourself at risk when getting involved with lunatics.
I would have more likely reacted by putting an exaggerated dumbfounded look on my face and then turned my disgusted look back & forth between the mother and her monsters. - But some people have no shame and they probably would have continued their bad behaviors with their mother's blessings. I'm sure she thought they were being 'little darlings'.