An Etymological Dictionary of the German Language/Eltern
Eltern, plur., from the equiv. MidHG. (seldom occurs) ęltern, altern, plur., OHG. ęltiron, (altron), plur., ‘parents’; corresponds to OSax. ęldiron, Du. ouders, ouderen, AS. yldran, OFris. aldera, ‘parents’; the plur. of the compar. of alt used as a subst. in West Teut. only. In AS. the corresponding sing. yldra in AS. denotes ‘father.’ For a similar evolution of meaning comp. Herr, Jünger.