From what we've dug up, this NM seems to come from an old Grimm Story. I've only found refernces to it in Spanish or translated from Spanish, but it seems to be a third installment from "The Elves and the Shoemaker." Los duendecillos translates to the elves. The third story involves a changling (that sound eerily like a taru) being swapped for a human child by elves. I found a great translation at http://www.grimmstories.com/language.php?grimm=039&l=en&r=es.
Which begs the question: If you boil water in an egg shell in front of a taru, will he go away?