This is from Hv:  Jiaogulan to keep up your immune system. Andrographis is the best herb I know of for the flu. You can make the tea and gargle with it for the sore throat and drink it for the flu. If you want to make it taste better add a little licorice root, which is anti-viral, immune stimulatory and anti-inflammatory. Propolis sprays are great for sore throats. Watercress is also a great anti-viral and anti-inflammatory. Also great for keeping the lungs clear.

Don't be shaking hands and wash your hands frequently using  a paper towel to turn off water and open the bathroom door so you are not touching dirty surfaces with your clean hands.  And try to avoid touching your eyes, nose or mouth with your hands since these are the entry points for the virus.

Most importantly though is to not stress over it. Stress really tears down the immune system. And you want to focus on building up your immune system and keep it strong.

Antiseptic wipes and hand cleansers would be a good idea since they will be in contact with other kids sharing items, shaking hands, etc. and will not always have access to water to wash their hands.

As far as supplements to help maintain their immune system I would focus primarily on vitamin C sources and zinc.

Andrographis is great if they actually come down with the flu.