I've been planning on starting a blog for a while...except it's to be about astronomy and observing the night sky; definitely nothing about my personal life.! As an internet user I am far more privacy-conscious than my peers, and although my "A/S/L" (ahem) isn't very hidden, I would never dream of giving out my full name, street address, telephone number, etc. to people I don't know personally.
If kids want to learn about the world, there are far better ways to do so than blogs: I think most news-articles and well-written opinionated pieces should suffice. And as far as expressing oneself is concerned, I'm sure there are well-policed sites meant specifically for kids/teens to discuss issues that interest/concern them...and, of course, there's the FunTrivia forums.

(Let me take this opportunity to thank the moderating and administrative staff of this site for making this as a safe a place as it is.)