If I'd been in a immigration hall when such an incident took place I would have gone straight to the nearest booth and told the guy that some idiot was threatening a woman and two children. The Police would have attended within 30 seconds.
Well, I do wish someone like you had been there as none of the several hundred people in the hall lifted a finger. So I had to do it myself. When the yobbos saw that I would not be intimidated, they backed down.
Of course it was a risk - and I was petrified - but saying or doing nothing was a greater risk, because it would have failed to set a boundary before physical assault. I didn't think they'd risk striking me there and then because of the potential witnesses and lack of escape route - I was more worried about what might happen later in the scrum of the baggage hall if it was not nipped in the bud.
In my professional life I have now and again found myself in some deeply unsavoury situations and, yes, I've sweet-talked or bluffed a few angry gorrillas (of the human variety). I may be a bit out of practice, but what I did learn from all of my past life is that the key is to dominate the situation quickly, making the other person believe there may be more or greater consequences than they had anticipated - and from an authority more substantial than me!
Jo Frost, btw, is 'supernanny' - famous for her no-nonsense discipline with toddlers. My little joke.
In retrospect, I should have said nothing and immediately walked away with the children to the head of the queue at the immigration box and asked them to call the cops there and then.
However, the moral remains: don't rely on other pax helping you, because they won't.