My kid seems downloaded 4 apps (or some extension within app) 2 days ago and money is taken from my bank account. I haven't receive any email from Apple about this purchase. And I don't see any Purchased items in my Appstore. I need help to refund.

If you are using Family Sharing and your kid downloaded them on their account, then the associated subscription is tied to their account and must be cancelled form a device signed in with their account.

In that case you wouldn't receive any email from Apple and instead it would be sent to the email account for the Apple ID that downloaded the apps and started the subscriptions.

Check the subscriptions from a device signed in to the child's account:link-> How to cancel a subscription from Apple - Apple Support

Speak directly to Apple.

Get Support -

https://getsupport.apple.com/

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