Contact iTunes store support and request for a refund:
They may also need your order numbers so it's best you get them ready.
You can find your order numbers on your email receipts and in your Purchase History. If you need to review your Purchase History, follow the steps in this article:
Hope this helps. =D
To prevent this from happening again, turn off "In App purchases" in the Restrictions settings on your iPad. You may also want to turn off the ability to install apps, to prevent purchases in case the child gets hold of your iTunes Store account information, and set the password to be required immediately. For more information, see: