Sorry if I’m in the wrong section here…
I'm looking for a book I read as a young teenager. Not having a lot of luck: I've Googled, Quora-ed, and so forth.
It is a children's book set in Holland. Two English children befriend two Dutch children (they have a wicked uncle).
The book has an English family (as I recall) and the parents have to go away for some reason - the English girl and boy befriend a Dutch brother and sister (possibly called Jan and Marieke). They vie with a wicked uncle to find some papers (I think). These are eventually found, caked in mud.
There are some phrases I recall: “Oh! Pofferjties!”; “looked like raw sausages floating in milk”; “washed their hands but only just above the wrists”. Also the uncle catches one or more of them, and gags one with a “dirty handkerchief”. There is much made of marshes, and the unfortunate kids are tied up and gagged on the sand.
I imagine it would have been written in the 50s (certainly after the war) and set in that time.
If anyone thinks this rings a bell I'd love to find it again.