Use these links to resolve your issue:
Read how to "Request a refund for apps or content that you bought from Apple" click here--> https://support.apple.com/HT204084
To directly proceed to "Report a Problem to request a refund" click here --> https://reportaproblem.apple.com/?s=6
If a reporting a problem request is unsuccessful you can also try clicking here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product.
Apple's terms of purchase for most countries are effectively, "All Transactions are final" (check terms at: https://www.apple.com/legal/internet-services/itunes/us/terms.html ). Apple may refund on a case by case basis, but realize they can also say no.
Use Restrictions on your iPhone, iPad, and iPod touch - https://support.apple.com/HT201304 - "You can use Restrictions, also known as parental controls, to block or limit specific apps and features on your iPhone, iPad, or iPod touch, including access to explicit content in the iTunes Store."
or just set a passcode on your phone which is not a toy.
Use a passcode with your iPhone, iPad, or iPod touch - Apple Support - hhttp://support.apple.com/HT204060
Or set your phone so it requires you enter your password in order ot buy something from the stores.