Would you intervene?

[gypsysoul]

Hope everyone had a great Christmas.
Sorry to bring up such an unpleasant topic but:

My brother was out shopping in the post Christmas sales today and came across this scene in one shop - a couple were out shopping with a girl aged about 8, presumably their daughter.
Something happened/was said and suddenly the woman/mother yanked the girl’s hair so hard the girl lost her balance. the woman then punched the girl in the back. Then for good measure the man/father kicked, yes kicked the girl.

My brother was shocked as were other onlookers. One woman intervened and gave the couple a good telling off.

So, what would you do in these circumstances? Intervene or ignore it?