In Westphalian death records, you often find "Kinderschreck" or "Kinderschrecken" given a as the cause of death. I tried to find a proper English translation ("children's fright" would be a very direct one), and the best one I could come up with is the classic "bogeyman".
When small children died, you'll often read that they suffered from "Krämpfe" ("seizures") or "Kinderschrecken". Both diagnoses are not very specific. When a child had convulsions, at least you could tell that something was wrong, even if the little one hadn't learned to speak yet. But there were always children who died without any obvious reasons. Compared to today's ICUs, medical knowledge was still underdeveloped, plus there was no social security system that made sure sure everyone had the financial means to afford a doctor's fees (many families were happry if they were able to pay the midwife) - if a doctor was available at all. Remember, this was (and still is) a pretty rural area.
So you can imagine that the cause of death remained undetermined often enough. Of course, they could have written "undetermined", but I guess it's in the human nature that you want an explanation when your loved ones die unexpectedly. "Undetermined" is unsatisfactory.
And that's where the Bogeyman comes in...