Girls, hello everyone, can you tell me what kind of chair your childre…

Girls, hello everyone, can you tell me what kind of chair your children have in our age group? The thing is that my son has a bowl-shaped stool, not formed and lately the color changes, one day it might be black, the next day green, then back to normal color, it wasn't like this before, he eats everything from the common table, in general I don't know what to do anymore, has anyone encountered something like this?