First off, no reputable Pagan Elder is going to encourage any child to hide things from their parents. Most Pagan religions are very family intensive and believe strongly in the bond between Mother and Child specifically. Hiding things from your parents can only disturb that bond. It is also very dangerous. I am not going to pretend there aren't freaks out there that use Paganism as an excuse to do things that are morally wrong or illegal. Hiding your actions from your parents puts you in a very bad position when you run across people like this.
Unfortunately, when we are children we do not have the freedom to do what we want as often as we'd like. There is a reason for this, though. Our parents are responsible for us and we are (whether we believe it or not) often the most important thing in their lives. They want to protect us and do what is right by us. Even if they don't give a damn, by law, they have to protect us until we are 18. Period.
Thus, in order to preserve the domestic tranquility of the Hearth Haven- the home and family- I suggest you do not try to hide anything from your parents. Many people think their parents will "kill" them if they find out they are doing something of which they don't approve. This is mellowdrama to say the least, but believe me, if they find out by accident, it will be much worse for you than if you tell them up front. If they forbid you, don't throw a tantrum. It just makes Pagans look bad. Simply abide by their rules until you turn 18 and move on from there. You can still hold the Gods in your heart and celebrate Nature in your soul. You don't need paraphernalia to be Pagan. Practice meditationi and acting with awareness and when you are legal, you'll be ready to dive right in.