Are the cows on fresh pasture? Sounds like typical milk scours to me. Good grass or a hot grain ration will cause it. Maybe even the cows eating alfalfa. Don;t know about the alfalfa, but the other 2 are very common.
Keep an eye on them. It has been my experience that the calves do not need to be treated in this situation, they will adjust on their own. So long as they continue to appear healthy (which they should), there is little to worry about.