I’m not a parent, but going by pop culture, it seems like literally every child has the same fears.
In pre-modern times, I imagine that they’d be sleeping in the same room as the parents, but if modern notions of privacy don’t permit that, seems we could at least design an enclosed capsule or something.
If it wasn’t those, it would be something else. There’s always something that will cause fear and it won’t help anything to remove everything that upsets them, especially in preparation for the real world. We see how it doesn’t work very well with overprotective parents who try to “protect” their children from everything. Those kids usually grow up maladaptive to the real world.
But if it’s not under the bed or a closet, it’ll be the jacket on the chair in the darkness or the tree limb in the dark outside of the window.
What happens if the kid goes to a friend’s house who doesn’t abide by these same rules? What happens if something happens to you and the kid has to be put in foster care or with a relative who doesn’t practice the same?
Similar goes for picky eating. Few things are tasty by default, but most tastes are acquired by repeated exposure to new cuisine.
I’m still getting used to clams, snails, slugs, and calamari. Went from gag reflex and unable to swallow to capable of eating but not savouring in a few months time.
And again with fears, it’s not that dark voids have become less dangerous or fearful, it’s just that I have checked enough voids to not be immediately alarmed.