Accidental in app purchase by minor
You can request refund on the website Apple Support, selecting "iTunes Store" product and "Unintentional/unauthorized In-App Purchase by a minor" topic.

Here is a good article for this case: http://www.macworld.com/article/2140066/how-to-get-an-app-store-refund-for-kids-accidental-in-app-purchases.html