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.
I always told my kids the monsters were in the closet not under the bed. I also introduced them to hand puppets named chewy and Bytee. They were monster ostrich that lived in the closet, there favorite food is my kids which they nip at and the kids all have found it hilarious over the years. Also there was a monkey that slept in the closet when the zoo was closed. I told the kids I was renting out the closet space. Have three kids 13, 11, 4 none of them were ever afraid of the closet or under the bed. Any hint that they thought something was in the closet and I would go full conspiratorial and confirm there is “something” in the closet. That always seemed to work well apposed to denying their fears.