How long does it take to receive a refund for an accidental App Store purchase?

Check out this Support Article:

If your refund is approved, the funds are applied to the same payment method that you used to buy the item. Here's how long it takes for a refund to appear on your account or statement:

• Store credit—It might take up to 48 hours to see the refund in your Apple Account balance.
• Mobile phone billing—It might take up to 60 days for the statement to show the refund. Processing time might be affected by your carrier. You can contact your carrier for an update.
• Credit and debit cards, Apple Pay, Apple Cash, and all other payment methods—It might take up to 30 days for the statement to show the refund. If you don't see the refund after 30 days, contact your financial institution.

Check the status of a refund for apps or content that you bought from Apple - Apple Support

If you want to review the purchases by your son before they are made, then you may want to check out the Ask to Buy option. Refunds are not guaranteed, so this is a good way to not allow any charge in the first place.

Approve what kids buy with Ask to Buy - Apple Support

Approved refund requests take up to 30 days for most payment methods. Click here for more information.

If it's already been that long, ask your financial institution or the iTunes Store staff.

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