Bad diarrhea in kittens

I'm responsible for a litter of 6 kittens, but have someone else fostering them, and they have really bad diarrhea. We've had them almost 2 weeks and they've had it the entire time (and were having it in the home I got them from). They're about 13 weeks old, have tested negative for worms, FELV and FIV. They have been on Albon Plus since Sunday, and 2 of the kittens also got antibiotic injections to help the diarrhea (I didn't take all the kittens in to the vet, just 2 of them), but it doesn't seem to have done anything.

They are getting Purina Kitten Chow mixed with a higher quality kitten dry my friend had, and are now getting Chicken Soup for the Kitten Lovers Soul wet (they were getting a low quality adult tinned food) and small amounts of mashed pumpkin to try and help the stools form.

They are incredibly healthy and happy otherwise - they all play and wrestle like mad, then will come and snuggle in the closest lap once they're done.

I'm going to give it another day on the Albon, and if there's still no improvement, take them back to the vet.

Anyone have any suggestions on what else it could be, and what I could try?

Have you had them checked for Giardia or Coccidia? My little boy Bamf has had soft stools (sometimes runny ) since I brought him home almost 7 weeks ago. He has been mostly active and playful the whole time, and eats and drinks and is not dehydrated. The vet just had his stool checked for Giardia and Coccidia because we dunno what is causing it, but he came up negative.

So I don't know what to do about my boy but maybe yours have one of those icky parasites?

They're on Albon Plus which treats coccidia, but they haven't been checked for giardia. I just spoke with a vet tech who said to give it a few more days for the Albon to kick in, then if there's no improvement, to bring in a kitten, the vet records and a stool sample and they'll look at them again and test for giardia.

I just spoke with their foster mum and she thinks that the poop isn't quite as liquid today, and they haven't had any "leaking" from their backsides in the last day which they have had since they get there which is good. Poor babies!