how i can refund apps

Refunds for what ? You can try contacting iTunes Support and see if they will refund or credit you : 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

If they are in-app purchases then to try and stop it happening again you can turn off in-app purchases on the device via Settings > General > Restrictions