How do I know if my son needs antibiotics for his diarrhea? Most often he is not given but there was one instance before that an antibiotic was prescribed.

The most common cause of diarrhea among children is a virus called rotavirus which will go away by itself but may cause dehydration.  So the management is replacing the losses with oral solutions and certain micro and bioactive nutrients to reduce the course of the illness such as zinc and "friendly bacteria".  There are only a few indications for antibiotics in diarrhea and they are those associated with bloody diarrhea such as  bugs called Shigella and Vibrio cholera, protozoa called Amoeba and Giardia