Grandpanow that was unfortunate for that mum, and I agree the looks woukd not have helped.
However that is a somewhat different situation than some I have observed:
*Child throwing food around and on floor , parent does nothing, leaves, mess everywhere for cafe to clear up
*child running between tables, knocking tables, crawling under tables where others are sitting, coffee on other tables getting spilt when table knocked
*child completely ripping apart small Central table decoration
*child having huge tantrum and instead of being held gently or picked up and taken out until calmed down, they were ignored whilst they tipped the whole table over!! Then watched whilst they flung themselves around the floor
The point os, it's not about children having tantrums, that's normal! It's about adult responses to those! It's not about children misbehaving per se. It's about adult responses to that!
In cafes etc it's about children needing to be taught and to learn about care and consideration of other people and their property...if they don't learn it over time they will certainly struggle as they grow up, when people will tolerate a self absorbed and selfish adult!
Having said all that I have also often observed children having a tantrum and being dealt with patiently and appropriately by gheir parents, children being quietly told/helped to pick up something they have deliberately dropped, children being quietly removed to discuss a problem. I suspect that we tend to remember the ones causing the hoo-ha with parents who let them rather than the ones who are quietly getting it right!