Unborn children are not part of their mother’s bodies, and they are not parasites. Both claims are scientifically inaccurate.
From conception onward, pregnancy involves two (or more) separate bodies. At no point in pregnancy is the developing embryo or fetus simply “a part of the mother’s body.” Every cell of the unborn’s body is genetically distinct from every cell of the mother’s body.
Although an unborn child does obtain food and shelter from its mother, this alone does not make it a parasite. You can not make conclusions depending on comparing characteristics. Most medical dictionaries define a parasite/parasitic infection as: “a pathologic invasion of one species by another that spends part of it’s life cycle in the host and obtains nourishment from the host.” Any normally-occurring single or multicellular organism that naturally inhabit the host are not included (and the womb is the natural habitat of a new human being). The difference between a fetus and parasites is that the fetus isn’t a foreign creature because it’s DNA is human DNA — it’s the same species - what we have is a human growing inside of a human (which got there because a man and woman joined their sperm and ova, which is a perfectly natural part of biology). It is perfectly correct to say the zygote/embryo/fetus belongs in the womb. Parasites, meanwhile, are not human and they were not created by a human male and female joining their sex cells together. In addition, parasites replicate in the host to form new offspring, but this does not occur with a fetus. Also, once out of the uterus, a fetus does not crawl into another one like an infectious parasite.