It must be labelled human grade / food grade. The other types are dangerous to cats.
I'd still use a flea comb and perhaps very carefully some not to sticky scotch tape to gently dab at the fleas on the kitten. If you put things in a priority getting food into the kitten and having bowel movements is going to be a priority for the kitten to live.
I think there are several types of diatomaceous earth. Not sure they are all safe. If the baby can get enough strength a second bath in Dawn would be better.