It's creepy as fuck, but not really logical. (Yeah, I'm looking for logic in an urban legend...) I like the theory that they're demons, but if they're powerful enough to appear as children, why can't they disguise their eyes? And if they want to trick you into letting them in your house/car, why do they creep you out instead of making you feel sorry for them? If they can go onto your property to knock on your door, why do they need your permission to enter the house? They're already in your space without permission.