I would cancel.
Then again, I went to a party where one three year old had rotavirus (I later found out she had thrown up once the night before). After the party two children wound up in the hospital with dehydration due to rotavirus, including my then 18 month old son.
After reading about rotavirus, I found it is very contagious, it can live up to 10 days on a hard dry surface (and even longer on soft wet surfaces).
After my rotavirus scare, I didn't host a playdate until my child had been symptom free for over twenty four hours *and* I had a chance to disinfect all his toys and steam clean the carpet that he had thrown up on.
"Each year in the U.S., rotavirus is responsible for more than 400,000 doctor visits; more than 200,000 emergency room visits; 55,000 to 70,000 hospitalizations; and between 20 and 60 deaths. Rotavirus leads to about $1 billion in health care costs and lost productivity per year in the U.S. Despite efforts to improve the management of childhood rotavirus-associated diarrhea, hospitalizations of children in the U.S. with the disease have not significantly declined in the past two decades. Hospitalizations are the most severe and costly outcome of rotavirus disease in U.S. children."