From the Online Etymology Dictionary:
The side playing games with language is the side trying to dehumanize unborn children, by replacing ordinary English with intentionally-obtuse technocratic jargon. As George Orwell wrote in his 1946 essay Politics and the English Language, “The inflated style itself is a kind of euphemism. A mass of Latin words falls upon the facts like soft snow, blurring the outline and covering up all the details. The great enemy of clear language is insincerity.” Words like “fetus” have been coopted to avoid calling unborn children “children.” [Of course, even “fetus” refers to the living-but-unborn offspring of an animal (e.g., a chick, while still in her egg). But that's a topic for another day.]
child (n.) Old English cild "fetus, infant, unborn or newly born person," from Proto-Germanic *kiltham (cf. 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 (e.g. Latin liberi/pueri).