I would like to explain the function of these blankets. They are not for sleeping they are for rolling the child in it when they are in need of calming. At least we don't use them for bedding. When Zach was younger he would climb in between the bottom sheet & the bare mattress. It would do the same thing with blankets on the bed. He would find an edge and tunnel under all the bedding. It soothes his nerves.
It is sort of like when you have a migraine and you retreat to a dark room. It is a sensory issue not necessarily bedding. It is a tool to use when they have a hard time dealing.