One of the saddest things I ever witnessed was on a bus - a little one, about 15-18 months, chattering away, like they do, mostly nonsense but you could make out the odd word. His mother said to him "will you shut the f**k up, you're doin' me 'ead in and I can't understand a bleedin' word."
And I also saw a mother give her child a really vicious back hander across the face, nearly knocked her over. The child's 'crime'? She'd dropped her ice-cream and was crying
We can all lose our rag and be OTT with our kids - I'm not blameless there, but some things really can't be excused.