You're trying to give the child a real, physical association with money. He pressed a button on the computer that let him customize his game, and now his parents are upset. If you just tell the kid, "Well now you have to mowe 7 lawns & your debt is payed," that's just punishment without demonstrating why the behavior shouldn't continue. If he can earn money and willingly pay his parents back, it's a controlled way to communicate that money represents work done - not just a different point to spend in a game.