All of this is very creepy; one gets the impression that some humans are "hunted", so to say.
I had this idea too. Hunters go out for the best game, they often want specific kinds of game, and humans often just hunt for sport. It might be the same for 4d-> 3d right?
There's always been a "mischievous" element as well. Like whatever force took/killed kids, delights in the parent's suffering: in them never knowing, and even getting the blame. The trickery of putting bodies back in places already searched. The whole confusion that ensues might be entertaining for them.