Before revision: The ancient plural of child was "cildra/cildru", to which an -en suffix was later added when the -ra/-ru became unproductive; 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 sole plurals such as Kind/er.
After revision: The ancient plural of child was "cildra/cildru", to which an -en suffix was later added when the -ra/-ru became unproductive; 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.