Examples of this can be seen in the history of English and Dutch. Historically, the general English plural markers were not only -s or -en but also (in certain specific declensions) -ra and -ru (which is still rather general today in German under the form -er). The ancient plural of child was "cildra/cildru", to which an -en suffix was later added when the -ra and -ru became unused.2 The Dutch plural form kind-er-en and the corresponding Zeelandic form kind-er-s are also double plurals which were formed in the same way as the English double plurals, while for example German and Limburgian have (historically conservative) single plurals such as Kind-er.
Breeches is an example involving an old plural that did not use a suffix. It was formerly breech which came from Old English brec which was the plural of broc.
Nordquist, Richard. "Double Plurals in English". ThoughtCo. Retrieved October 28, 2024. https://www.thoughtco.com/double-plural-grammar-1690409 ↩
Moylan, Peter. "Double Plural". Peter & Lynne's place. Retrieved October 28, 2024. http://www.pmoylan.org/pages/articles/language/Double_plurals.html ↩