What Causes Loose Bowels And Vomiting In A Child?

My son 3 years of age with 15 KG is passing watery stool since morning today for almost five times. We have given him Eubalanz one time. He vomited once during the day as well. His apetite seems to be poor right now. How do we sto his loose motion immediately? can we give him some medicine like veeflox etc..