Maybe it's because our children have to play/go to school/grow up with their children?
I for one don't like to have my teenaged children hangin' out with kids whose parents are too self-involved to pay proper attention to their progeny. That would also go for teenaged children whose parents conceived them so late in life that they were 'out of it' by the time the kids hit the dangerous adolescent years.
Not that I plead guilty to your epithet 'busybody,' but I sure as heck will be judgmental.