http://www.babycentre.co.uk/a1040566/what-to-do-when-your-toddler-screams
Why does my toddler scream?
Believe it or not, your toddler’s volume isn’t turned up high to annoy you, but because she’s full of energy. She’s exploring the power of her voice, and experimenting with what she can do with it.
And why does she always let rip when you’re at the supermarket or the museum? It’s because there’s a lovely echoing effect when you scream in big open spaces!
Some toddlers scream whenever they want their parents’ attention. It’s their way of saying, “Hey, look at me!” Others scream when they want something they can’t have, such as a biscuit or a friend’s toy. In that case, the shrieking means, “I want my way. Give it to me now!”