Samsung Galaxy S Advance — Play Store refunds

Foolishly I allowed my grandson to play Angry Birds on my Galaxy Note 2. He ordered a game worth £13.99 and within a few minutes he had bought one costing 69 pence. I have changed my settings so he can't do it again, but is it possible to have a refund. If so what on earth do I do to start the ball rolling.

Thanks

Pam McDonald