I'm not sue it was temper tantrums that were being mentioned earlier, which as you say can be fairly explosive and unpredictable.
It was more about the parents who take their children to a coffee shop, or other place that isn't a playground, and sort of detonate them into the previously quiet enjoyment of anyone else who happens to be there.
When I was a child (cue theme from
Hovis ad' ), even had I been inclined to run around a cafe screaming, my parents certainly wouldn't have allowed it. A proper upbringing means a child will know how to behave.
(

not yet 40 and it seems I'm an old fart

)
(ETA, cross posted there)