It is true that there is nothing ostensiby racist about this film or The Morning Bath, the Edison film made in imitation of it. The problem is that is an example of a stereotype that one encounters over and over again in representations of African American women or, for at matter, African or Indian women, bathing babies.
As indicated in other reviews, there is an implied racist joke in the whole idea of "a hard wash", of an infant that is hard to wash not merely because it is dirty but because of the colour of the skin. There is also a voyeuristic note in the way the audience is being asked - here quite explicitly in the catalogue description - to find the scene comical and laugh at (rather than with) the people represented.
Evidently, rather later when it became common to make films of white middle class babies being bathed (see my review of Baby's Toilet 1906), the content of the film and the regard on the scene were both very different. Here the bathing might also be very thorough but this time because it included powdering and weighing and all the things associated with best modern practice. Now, instead of being invited to giggle at the mother and baby, the audience is being invited to admire and emulate.