What Causes Nausea In A Child?

Well, there is apparently a stomach bug going around. My son didn t eat dinber last night and woke up at 2 vomiting. He has been doing so since. His throw up is white and he is like gagging bc he has nothing to actually throw up. Should I be worried and is there anything I can give him or 2 my other 2 kids so they do not gt sick. Someone told me to give my other 2 kids airborne gummies, do they work