Hello The child's upper teeth are rotting or I don't know what is…

Hello The child's upper teeth are rotting or I don't know what is happening, but some areas are clearly not there as you see And if the lower teeth are visible near the gums, they also rot and all the teeth, even those that have come out recently, have a white coating that doesn't go away Has anyone had this? What is it? What did the doctor say? How was it treated or is it treated at all?