I registered a sole proprietorship as a minor, and I spoke extensively with a tax attorney during the process. Here are some things to look out for.
First of all, minors can enter into legally binding contracts, but they can break contracts with no consequences. This doesn't mean you can steal customers' money or anything, but if you agree to sell something to a customer and the customer agrees to pay for it, you can decide later not to sell it to him and the contract will be voided. This concept is called disaffirmance. If money has exchanged hands, you would have to give it back. Keep in mind that only a minor has the right to break a contract, while any adult parties are bound to their obligation.
This may be dependent on the state, but at least in Missouri, I was required to register my business with the state. I also obtained a retail certificate, but I don't know if you would have to do that since what you are doing probably isn't considered retail. You should probably talk to an attorney or another expert to make sure.
Here's a big one: you can be sued for any damages resulting from your actions, and if you are registered as a sole proprietorship as compared to a corporation, there is no limit to how much you can lose. Even as a corporation, you probably wouldn't be subject to limited liability since you are the only person operating the business. Your parents will most likely be the target of the suit since you are a minor.
You will most certainly have to pay taxes, so be sure to keep very accurate records. You will, at a minimum, need to record all revenues and expenses, and I recommend getting some basic accounting software to help you keep track of everything.
Good luck to you, and keep in mind that anything I mentioned was specific to my situation, so be sure to contact someone who knows the law in your state to cover all your bases.