Parents: Why do so many kids have disorders and problems?

I know there's always been people with disorders and sicknesses and problems, but now it seems like there are more and more, and that if one kid in a family has something wrong, the rest of them are much more likely to be diagnosed with a problem, even if it's unrelated to the first one's. Is medical care just that much better than it was when I was a kid? Or are people just more neurotic, and push for diagnoses or self-diagnose their children? Or are problems more widespread for some reason? A combination? What's going on here?