There are two types of parenting. The parents who care how their kids act in public and the parents who DON'T care how their kids act in public...
My sister in law is the second type and I am the first type. If my son misbehaves in public, whatever toy/candy he was getting gets put back on the shelf and we are leaving. And if he's bad enough (which luckily has happened ONCE in his life) he will get spanked when we get home.
Today... At Dollar Tree, my niece was screaming and crying and throwing...