I'm sorry, I really, really am, but this is NOT a small lapse in judgement
You allowing your son access to your credit card is a HUGE laps in judgement.
Furthermore, and I know you're going to hate this, they shouldn't refund you at all because if they do, all you are doing is going open the floodgates with similar complaints from anyone who spends a lot of money and doesn't get what they want from the game.
Unlike you, I bet the other chap didn't open any packs or spend the currency, so EA refunded him I bet your "son" spent all the FIFA points, which is why they will tell you "sorry about your son, but no refund for you"