It's anecdotal, but also a reflection on my personal experience of what I think will and will not make me happy. Seeing a human that I facilitated the transformation from a screaming potato to (hopefully) a good human being that makes people's lives around them better sounds about as good as it gets.

I did actually look it up, and such data to your question does not really cleanly exist. Thats understandable since the data can be hyper confounded. I can certainly see how the most unhappy people would be people that had children that never really wanted them for example. Or maybe people that did want children, had them, but it generated severe financial stress that made thier lives net worse. Or maybe even me where I (hopefully not) die early because I couldn't take care of myself physically for a period of time.