Aha! I knew it! If you click on "info" above the Dutch text you get a pop-up that says "This rhyme has got the same melody as Twinkle, twinkle little star but quite another subject: a little girl called "kortjakje" (= short skirt) who stays "sick" in bed all the week behalf on Sunday when she goes to the church. The song does not tell that kortjakje is a whore, but the adults know it."
Perhaps now Wilfried will deign to post the lyrics (or links to them) of "Morgen kommt der Weihnachtsmann" and the "old bawdy student drinking song to this tune about a German knight drinking bitter with his henchmen." Bitte, Wilfried?