ubiquitin,
Very interesting point.
Quote from wiktionary:
From Middle High German narre, from Old High German narro (“fool, idiot, clown, stupid or crazy person”). Further origin unknown. Cognate with German Narr (“fool”), whence Dutch nar, Swedish narr, Estonian narr, etc.
The word may have been influenced in Yiddish by Hebrew נַעַר (ná’ar, “a youth”), though there is no need for this assumption.
If you search “קיין נאר” on otzar you get 229 quotes from seforim. For “קיין נער” you get 50.
The issue with the German theory is:
In the German, the plural of “narr” is “narren.”
In Yiddish, it should be “דריי נארן” or “דריי נארס.”
However, the plural term used in Yiddish נאראנים. Although this isn’t exactly Hebrew (which would be נערים) – this seems to be borrowing from the Hebrew style, which might show that נאר originates from Hebrew.
Similar to how one משוגענער (or sometimes משוגע’נער?) becomes two משוגעים (although משוגעים is pure Hebrew, while נאראנים is a mix).