Perhaps that should read 'what you do if anything' rather than 'how you react'.
The situation:
At my local station yesterday I was sat near a father and his two dc - a boy of around 9 and a girl around 7. I was sat near them for a long time because the trains were screwed.
The boy was mostly playing a game on his tablet making the odd comment and bickering with his sister but nothing to write home about.
The dad made a few comments to the boy initially which I found 
but figure that some families talk that way to each other in a jokey way. Started with:
- (in response to boy saying something wasn't fair) 'it's not fair I had to take two weeks off to look after you but life's not fair'
- 'lucky you couldn't talk by the time we decided to have your sister or we'd never have had another one'
And comments to this effect
Sometime later the dad had decided the boy was being disruptive and objectionable so took his tablet, got in his face and told him to stop annoying him, then pushed the tablet forcefully into the boy's stomach whereupon the boy started crying. The dad's response was to tell him 'come on, it wasn't that bad' and then to call his daughter over and start cuddling her.
The last thing I noticed was that, still determined that the boy was somehow causing a public nuisance, he whispered in his ear that he wasn'5 afraid to slap him in public if he didn't stop. I was sat close enough to here the threat.
I did nothing apart from silently judge and pity the poor boy.
So tell me. Was this abusive behaviour? If so, is there anything you would have done / said or does one have to pretend not to notice?
I am a wimp