What’s particularly instructive about this outré idea is that, of course, it’s not new. Among people who think about demographic seriously (as opposed to just popping off on a blog), the concept has been kicking around since the mid-’80s. It’s called Demeny Voting. Contra Yglesias, the goal of Demeny voting is to amplify the power of parents, since low-fertility countries often find themselves in a vicious cycle where the young are increasingly taxed to provide benefits for the growing proportion of aged, creating disincentives to have children, which makes the pension system even more unsustainable. But Demeny and the other grown-ups who’ve toyed with the idea realized that you can’t just hand the vote to 3-year-olds (they cannot read; they cannot get to the polls; etc.). So he proposed handing proxy votes to parents–an extra vote for father for every son, and for mothers for every daughter.
No country has tried it yet, but in the last year Hungary actually flirted with it in a semi-serious way.