This actually a legal question, but is a parent or guardian responsible for long distance calls made by a minor ?
Yes but you can ask the phone company to give you a break. Some times they will work with you. Ask for a manager or supervisor. And be very, VERY NICE!
Were the calls made from a phone on your account or does the minor have a separate account?
Yes. A minor cannot sign a contract for services. The parent must do so.
Yes. Who else do you think should pay? The child?