How cancel a subscription my son made

My son subscribed to paid YouTube, which bills monthly, but this app doesn't show up on my subscriptions. I got the email notification that it renewed automatically, hit the link, but the subscription doesn't appear anywhere! I've enabled the feature to ask before purchasing, but that is its own kind of a pain. How can it be possible that a service billing me $16/month is so hard to find and stop? Please help, what am I missing? The previous answers to a similar question assume that the subscription will show up in my list of subscriptions, but it absolutely DOES NOT.

Thanks!