I think it's because kids are online allot, (facebook & the thing with the bird) so they will naturally find new sites. This one, being a surprisingly popular site now days, is hard to miss. And if they have chickens (which is spreading like wildfire) well then there you go.......But most people on BYC now, I think are between 20-40 (or at least they seem to be.....) And what age do you consider members as 'kids'? I know many of our older member could refer to a 30 year old as a kid.....or are we literally speaking kids as in 10 year olds.
The way allot of people even find this site, is by searching a simple chicken question. The results for the search often include many links to BYC. They click on it, after they get what they need, they explore BYC, realize that they like it, and join.
I do also think that allot of the older members have left because of the technical things. This site is only more efficient if you know how to use it, and if your computer is somewhat fast. But they haven't really left, they still come on here, but just not as much, and they aren't as commercial or "postie" as they were before. I think this was because of the site change, but if you really think about it, the site upgrade was inevitable.