Would it be nice to return the Money? They entered in to a contract with a minor would was not the owner of the card. They can press charges it they choose, But they took on the risk by dealing remotely. You can not enter in to contract with a minor. It is legally invalid. That is the law. They are refunding since there only argument is they did not know they were minors. The Law did not care the contracts are still void.
Apple dealt with the same issues. They refunded and changed policy too. A big change when it affected the business model of in app purchases.
Is it even Facebook who received the money? These are app purchases. Facebook provides the platform but the apps are 3rd parties making the profit. For example, candy crush is owned by King who is now owned by Activision Blizz.