Headache, vomiting, diarhea...Is that a flu? 2 kids in our house have it, r we all infected by now?

Yes. Yes it sounds like you all have a viral syndrome. Passes from one to anorher.
Gastroenteritis. The vomitting and diarrhea with headache is usually caused by a virus, but not influenza (flu) although it is commonly called "stomach flu". It is important to take frequent sips of liquids to avoid dehydration. It is contagious.