Smelly diarrhoea and vomitings.

Hi dr I have three kids I traveled to my in-laws home with two of my kids after return from the day I came back two of my kids suddenly started vomiting and loose watery motions with stomach pain... I gave them ((OMH SYURUP DEROLAC ONDEM) )THEY STOPPED After two days I started vomiting and watery motions... I recovered got medicated... Kept saline ... AGAIN NEXT DAY ONE OF MY TWO KIDS AGAIN STARTED VOMITINGS AND MOTIONS VISITED PEDIATRICIAN HE ALSO KEPT SALINE AND SAME MEDICINE WAS PRESCRIBED BY HIM... MY THIRD KID WAS AT MY RELATIVE HOME CAME BACK ... HE ALSO STARTED SAME FROM THE NEXT DAY... I DON'T KNOW WHAT HAPPEN... DOES THIS DIARRHOEA AND VOMITING and fever ALSO contagious??? ??? I am really fed up what's going on I don't know