One possible confounder is that having children is a pretty much irreversible step. Whereas many people who don't have children might choose to have them later. So they regret their choice less, because it's a less final choice.
Another confounder is that parents with kids know what it's like to be single. Most people without children have no idea what it's like to have kids of their own. There is a subset that knows exactly what it's like, and it's those who have lost their children. Ask them if they regret their choice. Or actually don't, because people in that situation almost never made it there by choice.
Not having children is assumed not to be a final choice. But in many cases, it is. The more I learn about correlations between genetic disorders and parent age (including the age of the father), the more I feel I have been deceived about this.
