I was always told that if you whisper to a screaming child they have to shut up to hear what you are saying! I can't remember if it works though!

I actually taught pre-school (from 1-5 year olds at various times) for 3.5 years and I now teach college courses (and have for the past 5 years). Lowering the tone of my voice has always worked without fail in both the classroom and in any other sort of confrontational situation. And it was the method suggested by the owner and teachers at the pre-school. It's an inherently serious voice and shows the child you mean business. I don't think you want to be in a grocery store screaming along with your child. And, frankly, if someone pretended to cry or scream while I was crying, I'd be incredibly offended. But, we're talking about kids, they're probably screaming for a less than rational reason and are therefore not going to be offended by a tone of voice.

The easiest way to settle a screaming toddler is to make animal sounds. Bark like a dog or Meow like a cat. It confuses and distracts them. Next thing they know, they join in, they're laughing and forgotten what they were upset about.

Whenever my son gets upset I copy exactly what he is doing. If he screams and hits the cupboard because he wants a biscuit, I do it too and this seems to make him laugh and forget what he was screaming at!