During the 1920s, there was some artistic theme of posing young children, mostly girls, with no blouse on them. this particular child appears to have some sort of cloth wrapped around her chest, but I have seen others in which the child is not draped in any way. They all seem to have a necklace to hold or some other type of artistic element. I can only guess there was an art nouveau influence or trend that drove this.
To see other images like this one, click on “undressed” in the categories to the right.