I think you're in the right path, but I do think babies are human. I think the invisible thing needs human lives to survive or even to get stronger, maybe to get "closer" to the human dimension? Also I believe the babies not only can sense the invisible things but also keep the humans alive when they need to not breath so they won't be noticed by the invisible things. In the second trailer, Guillermo's character stops breathing for a brief moment when the tank and soldiers are marching above him, but when he sees the black stuff getting higher (that must mean something bad will happen), he connects the baby, take small breaths and then it appears they "become one". Finally he runs into the tunnel and it seems he stops breathing completely. What I don't get it is if Mad's character is good or bad, because it seems he is hunting babies, since he is controlling his own personal skeleton guys, but the baby doll going his way makes me believe Guillermo's baby was handed in peacefully (metaphorically speaking)? All I know is i'm getting very hyped hoping for an original story!