So you're referring to denial specifically for the reason of not having a bona fide marriage. I don't know of any couples who had children together who were denied for that reason.
However, you shouldn't assume that children provide a 100% guarantee regardless of the other facts or lack thereof. Suppose a couple has a child, but they have no evidence whatsoever of a relationship or living together before or after the pregnancy, and one parent shows no personal involvement or financial responsibility with the child. I wouldn't surprise if the GC was denied in such a situation. After all, there are careless people out there who have children with random strangers who don't see each again except to fight for custody or child support money (or to try to get a green card).