In app purchase made by my son (Clash of Clans)

Hey there, I have an 8 year old son who plays clash of clans on my phone. He doesn’t have his own so I let him put his face id so he can play the game as he hasn't really played on a phone before. (The face ID has since been removed.) But through my apple id my credit card is linked. It came to my attention recently that he used my card to make a few purchases. I spoke to supercell (who later told me to contact here) and my original plan was to fully refund the in game currency. Then my son tells me he spent the currency already, which I guess comes to no surprise. Ive read through your parental security information and I'm now taking the necessary precautions to insure this does not happen again unless with my permission. Is there anyway this refund could work? Without making my sons game unplayable. Im not sure how much of the currency he purchased, and if he goes into complete negative (respective to the amount spent), will he be able to still play? Im sure you guys can pull it up and see what he bought. I believe he made 2 or 3 purchases. Im assuming around $20 - $25 total. Thanks for the help!