Stomach flu is the most common cause of diarrhea and is almost always caused by a virus infection, which is usually ultimately harmless. Stomach flu is also called gastroenteritis.
Diagnosis can be verified with a stool sample. This, however, is rarely needed, as stomach flus usually sort themselves out with no further action required.
Most babies and toddlers have a period of stomach flu at least a few times a year. This is normal, and it teaches the defense system to recognize and combat diseases.
There is no targeted treament against the viruses that cause stomach flu. However, it may be necessary to take certain measures, as with all types of diarrhea. Your GP could possibly prescribe something. Especially in small children it is very important to look for possible dehydration phenomena. Small children with stomach flu lose a lot of water. Have your child drink plenty of fluids
From angelababy In Q&A