Kitten has diarrhea

I have two kittens (both age 8 months). One of them has diarrhea, but I don't know which one (found it in the litter box when I got home from work today).
Are there any home remedies for diarrhea in kittens? They both seem fine and are behaving normally, but one of them has diarrhea, and I can't tell which one. Is there Imodium (or other medicine) for kittens?
Thanks so much.

What are you feeding them?

The most common cause of diarrhea in kittens is parasites. Have they both been dewormed? If you have had them for a while, then I would look to the food. What are you feeding, and has anything changed lately?

I've had them since December (going on 3 months). Their food hasn't changed at all since I got them; I feed them a mix of kitten food (Fancy Feast) and this stuff from Friskies that has gravy in it (the box says it's for both cats and kittens). They were both dewormed at the vet back in December when I got them. They get fresh water.

They're both behaving normally, and the diarrhea seems to come and go; I noticed it in the litterbox on Monday and Wednesday, but not on Tuesday or yesterday (Thursday).