[aniketpanjwani]

Your wife's research is almost surely correlational, not casual - I'm assuming it's some sort of OLS using the NLSY or some similar dataset.

The fact that happiness and health goes up dramatically when parents are north of 60 just reflects that in the past - if you didn't have kids - it's because you didn't get married. If you didn't get married, it was far more likely to be because you were somehow unviable as a marriage partner than because you didn't want to get married.

So, you're going to get a spurious, strong correlation between happiness/health and the interaction between age > 60 and having kids. If you run the same regression among Americans in 30 or 40 years, that same relationship will not hold, since whether to get married and whether to have kids are to ever-increasing degrees explicit choices.