It hasn't changed, and some kids (or grown-ups who come across like kids) are on here. I don't mind. If I were to quit using HubPages, or quit looking at the questions/answers once in awhile, the reason would have nothing to do with any kids that post.
Sometimes smart, serious, kids will post on this site without posting their real age or by writing under an adult's account. Nobody would know a kid posted the stuff because the kid is smart and serious and writes well. Some stuff that looks like kids posted it is posted by adults who are either otherwise mature and just being goofy, or else adults who aren't the brightest bulbs in the batch. Either way, I didn't sign on to write here because I was thought I'd be writing for The New England Journal of Medicine.
It's the Internet, and HubPages has all kinds of people as members. Overall, it's a nice site, so I don't mind some kid stuff showing up. In fact, I've been known to join in occasionally. If the site were so over-run with foolishness search engine traffic were no longer sent to it then that would be a problem. For now, I think there's a whole lot less "kid stuff" going on here than on a lot of other similar sites, I can see someone getting fed up enough with the whole Internet-writing thing to stop writing online altogether, but as far as this, one, site goes; I don't the kid issue as being a huge problem for me, personally.