While brushing up on my Hungarian by reading through Routledge’s Colloquial Hungarian (the 2nd edition, which lives up to its title more than the 1st), I learned the previously unfamiliar word srác ‘guy’, the phonetic shape of which is somewhat unusual for Hungarian.
Searching through Google for an etymology took some work, but eventually I came across this article on the very subject at Magyar Narancs (a liberal weekly with a satiric touch roughly comparable to Private Eye):
In the 1950s srác was truly slang (just as csávó is now). The word is of Yiddish origin, that is, from the form of German spoken by Eastern European Jews, which is also the source of haver, szajré, a stikában and many other Hungarian words. The word derives ultimately from Hebrew sheretz (the plural form of which is shratzim), which refers to creeping, crawling creatures. This Hebrew word is found in the Bible at the very beginning, in Genesis 1:20, where it is used to describe the swarming of aquatic animals. Yiddish speakers, knowing Scripture, used this word in a comic metaphorical way, to describe groups of children (let’s not forget that in olden times there were many children playing together outside homes) as little swarms of creatures. Thus the word shratzim came to be used, later shortened to shratz. (The word entered German slang also as Schratz.) Today it is used only in Hungarian: in Yiddish the word did not put down strong roots, and Yiddish dictionaries published in the 20th century make no mention of it: it came to pass that in the 19th century it entered Hungarian slang (the first written attestation dates from 1888) and became entrenched there, while in the donor language Yiddish it was quickly forgotten.
As several sites I came across listed the word among Romani borrowings into Hungarian, I wanted to do some fact-checking, but indeed there is a German Schratz ‘child’ according to Heidi Stern’s Wörterbuch zum jiddischen Lehnwortschatz in den deutschen Dialekten with the same etymology (under the entry for Scheres), so it looks like the claim holds water.