Just because something is illegal doesn't mean it doesn't happen. With the latest introduction of chip and pin such things are bound to become more common. I gather they have been around for a while in the US but until very recently here the cardholder neede to be present in a shop to sign the credit card receipt. You would have a very hard time proving that you hadn't been the one to enter credit card details online. Personally I wouldn't let any of my kids within a hundred yards of my cards. Presumably if someone was using a card with your permission you wouldn't query it although the contract would technically be void if the seller believes they are dealing with the card holder. However if they send you goods in good faith it would be the card holders responsibility as they should keep the card from others or report it missing.