The image and the histogram suggest that the photographer used soft light, like a large soft box, above camera right to produce the flood of light on the subject with very soft shadows. Observe the catchlight in the subject's eyes and the soft shadows, especially under the tub, an area that "should" be in full shadow. There may also be a reflector or something providing fill on the left side of the image. The tones in this image are, as the histogram illustrates, primarily in the mids and highlights, with very little 3/4 or shadow tones. Makes sense. The light background, with separate illumination on it, brings the background up into this range. The choice of a caucasian child, white tub, and light background bring the tonal range up into a very narrow range. The image would be a lot different if, for example, a black background were used, or a spotlight effect were used for illumination on the child, etc. - these scene elements would increase the contrast and tonal range, changing the flavor of the image. The flood of bright, soft light is appropriate and appealing for the subject.
You could stretch the contrast for this image in post, but the feel of the image would change drastically.
kirk