Next step: what kind of disease _would_ explain this sort of pattern of deaths? In particular, the family with all the dead babies that finally got one to age five, one to age 3 and another one to age 1, at which point all three died in rapid succession. I was thinking, okay, maybe this _isn't_ agricultural, maybe they're in a city and it's cholera or something. It's too late for plague to be plausible. (Also, an unmarried adult man died in his thirties at sea gave me pause, but I'm treating him as an anomaly.)
A little research on the villages and towns in question killed the they're-living-in-a-city theory, because they're on Voorne-Putten. Hmmmm.
Malaria. Really. I have no proof, but the pattern looks about right, natural immunity would explain the weird selection of survivors and as recently as 1950 some people living in a retirement home in Rockanje contracted malaria. Was I expecting _malaria_ in the Netherlands (yeah, they _call_ it South Holland, but these things are relative)? No.
ETA: I don't know how or why I knew this, but I had this idea that a mother with malaria (even if she's doing okay with it) has trouble having living children. Googling suggests it is still a problem:
I'm sort of scratching my head about why I'm not finding any indication that this is a long-understood connection.
Language in this:
Suggests in fact that it's an area of ongoing debate! It looks like there is some difficulty disentangling malaria from co-factors that also lead to stillbirth.