the payment was made by the child. Can i get money back?

Use this form to make your request;

iTunes Support form -

https://support.apple.com/en-euro/itunes-contact

ASC - Late 2012 Mac mini, macOS 10.15.5; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5; iPhone 8+, iOS 13.5; TV 4th Gen, tvOS 13.4.5;  HomePods, audioOS 13.4.5 and Airport Express w/ Airplay 2

Apple usually considers all purchases to be final. But, if you have a problem with an a subscription or a purchase, see Subscriptions and Purchases https://support.apple.com/en-euro/billing. If you think you may be able to get a refund, then use the request a refund link. It will take you to Request a refund for apps or content that you bought from Apple https://support.apple.com/en-euro/HT204084

See How long refunds from the App Store or other Apple services take https://support.apple.com/en-us/HT210904

You also can get Apple telephone support for help in solving your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362Be patient; sometimes you can't get immediate telephone support.

And here is how to contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading Tell us how we can help.