Origin and history of kiddy

c. 1200, kide, "the young of a goat," from a Scandinavian source such as Old Norse kið "young goat," from Proto-Germanic *kidjom (source also of Old High German kizzi, German kitze, Danish and Swedish kid), a word of uncertain origin. The Old English (West Saxon) word for "young goat" was ticcen.

The extended meaning "child" is perhaps by 1590s ("I'm old, you say; Yes, parlous old, kids, and you mark me well!" in "The Old Law," by Massinger, etc.*), certainly by 1680s (see kidnap). In informal common use for "a child" after 1840s. It had been applied in slang to pugilists (by 1812) and skillful young thieves (1830s) as in the nickname of outlaw Billy the Kid.

IN slang language, a dashing person is often called a kid, or a kiddy. It is in fact, a synonym for a knowing one. ["Gentleman's Magazine," October 1839]

Kid brother "younger brother" is by 1890; kid sister by 1892. Kid stuff "something easy" is from 1913 (the phrase was in use about that time in reference to vaudeville acts or advertisements featuring children, and to child-oriented features in newspapers).

The skin or fell of kids was used to make a soft cloth, especially for gloves, slippers, boots. Hence as an adjective, "made of soft leather," as though from the skin of a kid (Middle English), but commercially by 19c. often in reference to material from calf or other skins.

Kid glove "a glove made of kidskin leather" is by 1670s; they were popular in aristocratic costume, thus kid-glove (adj.) had a sense of "dainty, elegant" (by 1856). It was commonly paired with silk-stocking and followed by gentry or aristocrat. Kid-gloved "characterized by wearing kid gloves" (hence "aristocratic") is by 1836.

Kid glove (v.) "handle in a delicate manner" (befitting of an aristocrat) is attested by 1913 (kid-gloving) from earlier phrases, e.g. "they will handle him in kid gloves, nothing harsher" [Vermont Patriot, Feb. 4, 1839, of a politician escaping punishment by his party].

* lechery, as well as youth, might be the notion. In the same brief speech he also calls them jack-boys, glyster-pipes, lank suck-eggs, weasels, and lecherous dog-bolts.

diminutive suffix used in forming in pet proper names (Christy, Sandy, Jemmy), attested by c. 1400 in Scottish (as -ie). Perhaps it is a merging of the common adjective ending -y (2) with old fem. suffixes in -ie. It might have been reinforced by Dutch -je in similar use.

According to OED (1989) it became frequent in English 15c.-16c.

The use with common nouns, childish names of animals (Jenny wren), etc., also seems to have begun in Scottish (laddie is by 1540s) and become popular in English from late 18c. via Burns (timrous beastie). But the formation perhaps appears earlier in baby and puppy, and compare hobby in hobby-horse. Granny, dearie, and sweetie all are 17c. and early 18c.

In general use with names of girls (Kitty, Jenny), where it coincides with names such as Mary, Lucy, Lily, where it is not a diminutive. The extension to surnames seems to be from c. 1940.