I'm writing a story that is your run of the mill boogeyman story. I'm having a little trouble finding Germanic monsters that ate children. There were witches in the Grimm's fairy tales, but not much in the ways of creatures of legends.
I did a little research and found nothing I would recommend you to use instead of germanic mithology to use Russian folclore or Nordic mithology instead. If not, you could adapt some home spirits and turn them erratic and mischievous. I am sorry I couldn't fully satisfy your question. Espiritu Noble
If you are willing to take your research to Iceland, you will find what you're looking for. Some VERY grim supernatural beings in their folklore. You may have heard of the jolly Icelandic Yule Lads? Well check out their mother Grylla (or Gryla.) She was ...well, just check her out. By the way, the title of this thread gave me the wrong impression. I thought you were writing about children who ate monsters! Sounds like a Plan. Here are a few pics of Grylla in her glory:
I see a lot of child thieves but none that particularly mention eating except the Roggenwolf. Here is a wiki page that mentions a lot of child thieves: https://en.wikipedia.org/wiki/Feldgeister. There are Ogres, although not specifically German the Germans did "know" about them.
So when I read the title of the thread I thought it was about children who ate monsters. To make it sound like monsters who eat children, it may need to be re-edited like this: “Children-eating monsters.” OMG, take a look at those images (above). That’s enough to fuel anyone’s nightmares! But in your case, @Kallisto , ideas for some scary stories.
Here’s something about Lamia, the child-eating monster of ancient Greek mythology. https://en.m.wikipedia.org/wiki/Lamia
I previously missed it on the feldgeister page I linked--the Roggenmuhme (she-demon) also eats children. Churns them into butter. Yum yum.