[CWJeff]

I've always had an even worse idea, ethically speaking, that I think would combine well with yours : the first generation would raise the third, as you said, but that third generation would be born out of the frozen gametes of the now deceased zero generation.

That way, embryos would only be created after the death of both biological parents, which would give you whole lives to look at to decide if you wanted these persons to reproduce.

That would open the way to some interesting possibilities in directing human evolution while opening a whole new world of horrific abuse and creative eugenics.