Diarrhea in rabbits is very serious. Please take your bunnies to the vet immediately. Rabbits have very sensitive GI tracts and can die easily to stomach upsets.
They are most likely having diarrhea due to something in their diet. Try changing it around a bit to see if that helps. If you recently added something, take it away and see if it helps.
You should see a animal Vet. The cottontails may need a round of antibodics to cure an illness or disease. Signs of diarrhea could also mean a problem with the food you are giving them or the water. Try switching them the food and water for 2 days and see if the problem is getting better.
