Refund in app purchase

First, 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:

http://support.apple.com/kb/HT4213

As to a refund, that's not automatic since the terms of sale for the iTunes Store state that all sales are final. You can contact the iTunes Store, explain the reason for your request, and ask, though:

http://www.apple.com/support/itunes/contact.html

They're usually pretty lenient in the case of inadvertent purchases by children. No guarantees, though, just as if your child was in a store and ate a bunch of food (in other words, something that can't just be returned).

Good luck.

All purchases are considered final but you can try the 'report a problem' link to contact iTunes Support and see if they will refund or credit you : http://reportaproblem.apple.com

If the 'report a problem' link doesn't work then you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

You can prevent in-app purchases on your phone via Settings > General > Restrictions > In-App Purchases 'off', and you can also require your password to be entered for all downloads.