K.B.
Have the kitten seen at the vet first and bring a fresh stool sample along. More likely the kitten has intestinal parasites - roundworms, Giardia, etc. It needs to be treated for those first before you start messing around with probiotics. I will use them for adult animals if I think they have something going on that probiotics will actually help, but in this case I think intestinal parasites and possibly adjusting to a new diet is more likely. With kids in the picture, it is very important to get the kitten treated correctly - some these parasites can be passed on to people if they getting even microscopic amounts of fecal material on their hands and then sticking their hands or fingers in their mouth without washing them. Don't try picking something up at the pet store either and treating the kitten yourself - take her to the vet. She will need an overall check-up to make sure she's healthy, a stool sample examined, and possibly started on vaccines.