dead man shuffle

You unlock your front door, and head outside. It's a warm day, you can even hear bird song; only humans were affected by this...thing.

You head into the middle of the street, heedless of cars; who's going to be driving now? You pull back the rags, revealing a child, face down on the road. Judging by the lump on the back of their head, they were hit and left to lie. You wonder why?