Hi, my dd and ds are friends with another sister and brother at school, they are in the same classes and often play at each others houses, etc. My friends two have both gone down with a sickness bug, and having gone through my fair share of throwing up over the past few months, I would hate them to come down with it, especially as I have an 18 month old dd as well. Is there anything I can do/give them to boost their immune systems or do you think it's too late?