My 5 and 6 y.o. came home last weekend with a stomach virus, they started back up again today. is it possible to be re contaminated?

Recurrent GI bug: The immune system 'should have' registered a specific response to the first illness, so it's unlikely it's the same exact virus as before. I think in your children's environment there are probably many different viruses (germs) circulating -and they must have acquired a new but slightly different infection. Either that, or they had so much exposure to the former virus, their system was overwhelmed