child cancer risk higher in richer rural families

I am a strong believer in exposure to bacteria to creat a healthy and strong immune system.
In this article they are saying that richer families tend to keep their children in amore bacteria free environment, and in doing so children in richer families have a higher cancer risk because of this. There are obviously many other factors here that have not been accounted for. Even so I am in support of any article that shows a link between exposure to bacteria and a healthy immune system.