A try you saying you can’t see the benefit to society of parents actually having time to raise their children? Not everything requires a peer-reviewed study.
I do see the benefit of parents having time to raise their kids in society. But I have also seen explicit comments on HN that people don’t have kids because we don’t have enough benefits. If the goal is simply “give people a year off so they can have their one kid and then be done with it”, so be it. But then we shouldn’t be advocating for these policies as a solution to anything besides giving parents a long paid vacation.
Even if there are benefits to society, there are also costs. To make sensible policy you have to know the size of both. And I personally have no idea how big the benefit is and would no doubt need several peer-reviewed studies to work it out. Maybe it's more obvious to you.