how can i cancel an order which i did not authorise?

my four year old daughter has purchased games on iTunes using my iPad 2. obvious;y she wasn't aware of what she did. i just learned all about this today when i received an email from iTunes with the payment confirmation (payment receipt). That application was billed to me @ $99.99. the transaction was made 4 times and i received invoice for each at the same amount.

i googled on how to cancel this order but it all lead me to "how to cancel pre-order". Really need help from anyone on how to cancel this order.