it wouldnt bother me in extreme circumstances,like if the child had run out in front of a car and the mother was obviously acting out of shock and fear,but today a boy of about 5/6 came out of asda with his mum and he either dropped or threw(didnt see)the lid of the bottle of water he was drinking on the floor.the mum slapped him round the head,knocking the water all over him,and shouted 'pick that up NOW!'.
i felt really bad for the little boy,but then i feel i had no right to judge as i used to smack dc1+2 occasionally when they were younger,before i learnt better ways of parenting.