Teachers and those who work with children: how do you keep from getting sick all the time?

My wife was only back to school for 2 weeks before she caught a cold. She seems to get sick so much. She says it’s the kids; they are always sick. I tell her to wash her hands and don’t touch anything that belongs to the kids, but she still gets sick. She says there is no way not to come in contact with kid germs.

How do you keep from getting sick?