Honestly, you are much too young to be worried yet much about it, though I suppose if you aim to be a child star... Anyway, in all honesty, you'd need an agent if you plan on jumping straight up, and this is not too realisticly possible. You should take part in smaller productions that can gain you experience and, when the time comes, tackle an american idol challenge.
Fame comes with a hefty price though cublet, so keep in mind what are doing.