Eight seems a little young, I think most start in their early teenage years. My own experience was to start with HTML and Javascript, and from there I moved on to Perl, C and the like.

I think HTML, Javascript, and CSS make a great starting point. Web pages are something you can show off to your friends--I got a lot of satisfaction from showing off what I had made when I first started out,

There's tons of books and resources to learn it. More importantly it's easy. You can't get HTML stuck in a loop, but it will still provide many opportunities for the kid to learn that computers will do what he says, not what he means. And all he needs is a text editor and a browser.