Just as Tay said, there's no way they can track down every single person who infringes on copyright. I mean, they can, but the repercussions of trying to catch that many people -- honestly, there are much more important things the government and law enforcement can be doing (trust me, I know -- I'm taking a Crime class at college right now). Also, it's not only stupid, but insane to try and prosecute someone under legal age for copyright infringement. They can argue all they like about the people in question understanding the consequences of their actions, however, in most countries the most they can do is send someone who is still a minor to juvie/somewhere equivalent. (I, however, would not be safe. But I don't share music, I only download anime -- mostly anime you can't buy in America). Also, they are cracking down more on feature-length movie and music sharing than anime, so most of us here shouldn't be too concerned (unless you download music. >_> )
However, it would still be a good idea for everyone here to be prudent about what they download -- moreso than usual.