An Etymological Dictionary of the German Language/Annotated/Eltern
Eltern, plural, from the equivalent Middle High German (seldom occurs) ęltern, altern, plural, Old High German ęltiron, (altron), plural, ‘parents’; corresponds to Old Saxon ęldiron, Dutch ouders, ouderen, Anglo-Saxon yldran, Old Frisian aldera, ‘parents’; the plural of the comparative of alt used as a substantive in West Teutonic only. In Anglo-Saxon the corresponding singular yldra in Anglo-Saxon denotes ‘father.’ For a similar evolution of meaning compare Herr, Jünger.