Here's how to request an app or media refund from Apple (From: Request a refund for apps or content that you bought from Apple - Apple Support - see the article for more detail.) If you bought this in the EU from a third party, see: About purchases not billed through the App Store or Apple In-App Purchase - Apple Support instead.
1. Sign in to https://reportaproblem.apple.com
2. Tap or click "I'd like to," then choose "Request a refund."
3. Choose the reason why you want a refund, then choose Next.
4. Choose the app, subscription, or other item, then choose Submit.
If you were charged for a subscription that you no longer want, you can also cancel the subscription using the directions in this article --> If you want to cancel a subscription from Apple - Apple Support
Read this support article for information about how long it takes to receive a refund (if you are granted one), and how to check the status of a refund for apps or content that you bought from Apple --> Check the status of a refund for apps or content that you bought from Apple - Apple Support
To avoid this in the future:
You may wish to always require a password for App Store and iTunes purchases.
Click here ➔ Require a password for purchases in the App Store and other Apple services - Apple Support
Manage App Store purchases, subscriptions, settings, and restrictions on iPhone
Change settings and restrictions in the App Store on iPhone - Apple Support
"You can use Screen Time to prevent unintentional or unauthorized purchases from the App Store and other Apple services. You can require a password for purchases, prevent certain types of purchases, or disable purchasing completely." - Use Screen Time to turn off in-app purchases on your iPhone or iPad - Apple Support See how to 'Use Screen Time on an iPhone, iPad, or iPod touch' by clicking here --> Use Screen Time to manage your child's iPhone or iPad - Apple Support