Moose is right...if it was a minor who "entered into the contract," the contract is not legally enforceable. Even if his parents consented, as Hans suggests they might have, the consent would have had to have been part of the original "contract", and I doubt there was a special provision in the "contract" including such consent. Parental consent would materially alter the contract, but genrally speaking, a material alteration to a contract, if oral (as this undoubtedly would have been), cannot be enforced. HOWEVER, if it was the kid using the parent's ebay account, then the "contract" is no longer a contract in quotes, it is a real contract and is enforceable against the parent. It would be up to the parent to "collect" from the kid (ha ha!).
It's complicated, but I don't know if you're completely out of luck, double M...