I am a nanny and I bring my almost 1 year old dd with me to work. She just got over being sick this weekend and when I got to work one of the kids was up all night with a stomach bug and the other has a cold. We never discussed what would happen if they were sick but I always assumed she would stay home with them. If it was just me I wouldn't care so much but the last thing I want is my dd to get a stomach bug. She didn't even warn me. Would that upset you?
Re: How would you feel?
I spent years as a nanny...the reason families get nannies versus out of home care is to prevent having to take sick days. It is a nanny's job to be there to care for the children when sick.
Unless you had clearly made it known you would not do this before getting hired then the parents had no reason to assume you would not care for their sick child.
Keep in mind that most illnesses are contagious before the symptoms are present so your child was exposed last week before being there today.
Bets you can do is extra hand washing and cleaning to prevent it from spreading. If you are really concerned you can have back-up care for your child for the days the other children are sick so you can work but your child can stay away...but again she would have likely been exposed in the previous days.