How do I remove my credit card from my child's payment methods?

My 14 year old son has his own savings and checking accounts with his own debit card and has asked that we remove our payment methods (credit card and PayPal) from his account so that he can use his own payments. I removed PayPal altogether from our payment methods so that is no longer appearing on his account. However, even after adding his debit card and PayPal account, my credit card is still showing as the default payment method for him. When I go to Settings -> Name -> Payment & Shipping, the "Edit" on that screen on his iPhone is unable to be clicked to update anything. He was removed from the family share account and that didn't change anything, my card is still his default payment method. Is there anything else I should be doing or does anyone have any suggestions at this point? I could care less if he uses my card, he's always paid me back, but he really wants to get this accomplished.