Hello NikolaJames,
Use these links to read about getting an app refund:
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. The terms say they may also deny refunds if they suspect abuse (too frequent requests). If your 3 year old can get hold of a costly item of equipment you should consider this -->
Require a password for App Store and iTunes purchases
https://support.apple.com/HT204030