Who seriously would do this to their child over a pinch? Get a grip.
You're really just trying to goad, aren't you?
Ok, I'll explain it properly.
Obviously, a pinch is not enough to call the police. A pinch would just require a "stop that, it hurt, don't do it again". Not a hard slap in front of everyone.
It really doesn't fall under "DV", just twattiness.
However, repeated hard pinches that leave marks would fall under DV.
If, as it was claimed, the poor mother suffered DV at the hands of her children the best response is not to slap their children. It is then, to cut contact, and if necessary to call the police.
A mother who slaps children hard in the street is not likely to fear her children, though. It looks more like lack of boundaries on both parts, as I wrote on my first post.