A theory I have on this film.
So, I have a theory about the non-humans in District 9. I'm not sure my theory totally works and it's kinda farfetch'd but I just thought about it and felt like I should share anyways. So, you know how Wikus slowly turned into an alien after being sprayed by that alien fuel? Well, my theory is that it implies that perhaps the non-humans (Prawns) are actually humans themselves. Suppose that before the events of District 9, a group of astronauts went out for space exploration and they found an unknown planet of an unknown alien species. They crashland on that planet and need a way back to Earth. Whilst on the planet, the astronauts are exposed to the very same substance and get mutated into the non-humans we saw in District 9. They steal one of the alien ships there to get back home. It took a while for them to get back (they possibly multiplied a bit while on the the ship hence, the kids). And once they get to Earth, they are unrecognised by the humans and are treated as such. That is when the film starts. Chistopher (being one of the mutated astronauts) knows that they cannot live this way on Earth and must search for a cure by leaving Earth and going back to the Alien planet they discovered. That is why he is also carrying a sample of the fuel, to study it before he leaves. Wikus is exposed to the fuel and starts turning into a non-human which is what supports this theory that these creatures started off human. That is why Christopher promises Wikus that he will cure him because he is also trying to find a cure. That is also why Christopher was unable to cure Wikus in the film because he knows he has to leave Earth before he can figure out how to cure them.
I know, my theory is a little out there but I thought I would share to see what anyone else thinks. Let me know your thoughts! :)