Old English eanian "to bring forth" (young), especially in reference to sheep or goats, from Proto-Germanic *aunon (cognate with Dutch oonen), from PIE *agwh-no- "lamb" (source also of Greek amnos "lamb," Latin agnus, Old Church Slavonic agne, Old Irish uan, Welsh oen). Yeanling "young lamb, kid" is recorded from 1630s.
-ling
diminutive word-forming element, early 14c., from Old English -ling a nominal suffix (not originally diminutive), from Proto-Germanic *-linga-; attested in historical Germanic languages as a simple suffix, but probably representing a fusion of two suffixes: 1. that represented by English -el (1), as in thimble, handle; and 2. -ing, suffix indicating "person or thing of a specific kind or origin;" in masculine nouns also "son of" (as in farthing, atheling, Old English horing "adulterer, fornicator"), from PIE *-(i)ko- (see -ic).
Both these suffixes had occasional diminutive force, but this was only slightly evident in Old English -ling and its equivalents in Germanic languages except Norse, where it commonly was used as a diminutive suffix, especially in words designating the young of animals (such as gæslingr "gosling"). Thus it is possible that the diminutive use that developed in Middle English is from Old Norse.