Rae seems to have no parents, or even anyone to care about her, and walks blindly without supervision and without anyone seeming to care or even noticing her. The world around Rae is beautiful and serene, but strangely devoid of people despite plenty of houses and infrastructure, with a grand total of six human characters seen in the entire game, including Rae herself. Only Lily even reacts to her, the lawnmover man and the dog owner disappear immediately after a glimpse of them, and the food seller and the gravedigger ignore Rae entirely and just keep doing what they're doing, forever.
Furthermore, there are some phenomena that are hard to explain by human interference. In Chapter 4, a truck blocks Rae's path back in a very odd fashion after she picks up the bread, but we never hear it driving there, nor ever see the driver. Then the fence gate spontaneously opens and then closes offscreen to let Rae return to the earlier area, while Rae is unable to open or close it normally.
It is unclear what killed off most humans, but it may have been either the same weird explosive sun that burned off Rae's eyes in the beginning, or technology going haywire — perhaps self-driving cars, and whatever opened and closed the gate. In any case, assuming the humans seen in the game are not the last ones left, there are probably enough of them left over the world to eventually repopulate and rebuild.