I do not have access to my son's Xbox One, how do I prevent charges?

You can also set the account to ask you before conpleting purchases. https://support.xbox.com/en-US/help/family-online-safety/child-accounts/approve-child-purchases

Smwutches, I am grateful for your help. This is exactly what I want but unfortunately, as I read the information your link takes me to, I have to do it on the physical Xbox, which I do not have access to.

I am surprised that there is no way for me to do this either online or via the Xbox Family app.

Smwutches ... any other thoughts? Thank you!!!

If no other way, if he won't stop the in-game purchases, then I'll take away the credit card and thus his game pass. Hopefully he'll learn a lesson.

Sign into his Microsoft account at http://account.microsoft.com and remove the card from his account. If it is tied to an active subscription, you would have to cancel the subscription before you can remove the card or wait for the subscription to end.

Hi,

you could request a call back from the phone support and ask them if they can change this setting for you. You just need access to the email account of the Xbox profile to identify yourself.

I don't know if they are able to do so but I think it's worth a try !

(sorry can't post a link cause I'm writing on my Xbox)