English is a pain to learn because it’s so irregular. Or is that because its so irregular?
So, for instance, one cow, one child; two cows, two children, not two cowen or two childs.
The productive method for making nouns plural in English is to add an “s” suffix at the end of the word. But wait! It turns out that the “n” suffix was used to make the plural of many other words, besides child.
We still have one ox, two oxen but it also used to be one shoe, two shoon and one cow, two kine.
So the phrase “kith and kin” (really, “kith and kine”) means “relatives and cattle” or, by extension, “family and property.”
Cows are synonymous with property and wealth in many Indo-European languages. The Sanksrit word “go”, Latin “bos” and English “cow” are all derived from the PIE *gwous. (Compare Latin “pecus”, ‘cattle as wealth’, also Sanskrit “pasu”.) The “kine” word is supposed to be related to “kind” as in the phrase, ‘payment in kind,’ meaning ‘payment in cattle’ rather than ‘payment in money.’
This productive “n” suffix is used self-consciously as a joke in computer terminology. So nerds refer to one computer as a box and two as boxen, or one old DEC computer as a VAX and two as VAXEN, or one inadequate vi alternative as EMACS and two as EMACEN.