Preventing unauthorized game purchases and bank account debits on iPhone

Use Screen Time to prevent your son from playing games.

click here ➜ Set schedules with Screen Time on iPhone - Apple Support

If you have setup Family Sharing and his Apple ID is part of your Family Sharing group, then set up Ask To Buy to be able to confirm or deny purchases from your device.

click here ➜ Approve what kids buy with Ask to Buy - Apple Support

What part of previous reply was unclear?

Again, if you have set up Family Sharing, use Ask to buy to deny purchases, or even turn off Purchase Sharing entirely. This will affect everybody else that is part of the Family Sharing group.

click here ➜ Turn off purchase sharing and stop sharing a payment method - Apple Support

If you have not set up family sharing, then you would have had to set up your credit card or other payment method on his account, and the only way to stop it, is to remove your payment method from his account.

click here ➜ Remove a payment method from an Apple Account - Apple Support

July8 wrote:

He has his own IPhone. How can I stop these charges for his games he plays on his phone from coming out of my bank account?

If you are using Family Sharing, see the link that Phil0124 posted earlier.

If you aren't, you could remove your payment method from your son's account.

You could also use Screen Time, a Screen Time passcode, and parental controls to try to block him from making in-app purchases at all – whether or not your payment method was on his account. I'm not sure exactly how to arrange things if he has, say, his own iCloud or Apple Music subscription (requiring some payment method to be on file), but you just want to block app and in-app purchases, there might be a way:

Use Screen Time on your iPhone or iPad - Apple Support

"You can create a Screen Time passcode to make sure the Screen Time settings you've set for yourself or a child's device stay in place."

Use parental controls on your child's iPhone or iPad - Apple Support

"You can prevent your child from being able to install or delete apps, make in-app purchases in apps installed from the App Store, and more."

July8 wrote:

He has his own IPhone. How can I stop these charges for his games he plays on his phone from coming out of my bank account?

Having one iPhone or having many doesn’t matter here.

Which Apple Account is used, and how that account and Family Sharing is configured, matters.

If you are erroneously sharing an Apple Account, this is one of many reasons why you don’t want to do that.

Everybody should have their own Apple Account.

If you are sharing an Apple Account, here is how to split the data:

• How to “unshare” an Apple ID - Apple Community

The links from Phil0124 include how to set up the son’s account, Family Sharing, and the purchasing restrictions.