Old English cild "fetus, infant, unborn or newly born person," from Proto-Germanic *kiltham (source also of Gothic kilþei "womb," inkilþo "pregnant;" Danish kuld "children of the same marriage;" Old Swedish kulder "litter;" Old English cildhama "womb," lit. "child-home"); no certain cognates outside Germanic. "App[arently] originally always used in relation to the mother as the 'fruit of the womb'" [Buck]. Also in late Old English, "a youth of gentle birth" (archaic, usually written childe). In 16c.-17c. especially "girl child."
The wider sense "young person before the onset of puberty" developed in late Old English. Phrase with child "pregnant" (late 12c.) retains the original sense. The sense extension from "infant" to "child" also is found in French enfant, Latin infans. Meaning "one's own child; offspring of parents" is from late 12c. (the Old English word was bearn; see bairn). Figurative use from late 14c. Most Indo-European languages use the same word for "a child" and "one's child," though there are exceptions (such as Latin liberi/pueri).
The difficulty with the plural began in Old English, where the nominative plural was at first cild, identical with the singular, then c.975 a plural form cildru (genitive cildra) arose, probably for clarity's sake, only to be re-pluraled late 12c. as children, which is thus a double plural. Middle English plural cildre survives in Lancashire dialect childer and in Childermas.
Child abuse is attested by 1963; child-molester from 1950. Child care is from 1915. Child's play, figurative of something easy, is in Chaucer (late 14c.):
I warne yow wel, it is no childes pley To take a wyf withouten auysement. ["Merchant's Tale"]
kine n.
archaic plural of cow (n.); a double plural (compare children) or genitive plural of Middle English kye "cows," from Old English cy (genitive cyna), plural of cu "cow." The old theory that it represents a contraction of Old English cowen is long discarded.
The Old Testament kine of Bashan, railed against in Amos 4:1-3 because they "oppress the poor," "crush the needy," and "say to their masters, Bring and let us drink," usually are said to be a figure for the voluptuous and luxuriously wanton women of Samaria, "though some scholars prefer to see this as a reference to the effeminate character of the wealthy rulers of the land" ["The K.J.V. Parallel Bible Commentary," 1994]. The word there translated Hebrew parah "cow, heifer." The cows of Bashan, east of the Sea of Galilee, grazed in lush pastures and were notably well-fed and strong beasts.
seamstress n.
"needlewoman, woman who sews or makes seams," 1640s, with -ess + seamster (also sempster) from Middle English semester "one who sews, one whose occupation is sewing," from Old English seamestre "sewer, tailor, person whose work is sewing," from seam (n.) + -ster.
The -ster ending is feminine, but in Old English seamestre also was applied to men, and the Middle English word was used of both sexes, though seamsters were "usually female" [Middle English Compendium]. Evidently by 17c. the fem. ending no longer was felt as such and a new one added (as in children, etc.), and seamster thence was applied to male sewers.