I did research it.. and the problem is they are contagious for up to a month. That is a long time to quartine them.
A half-century of antibiotic availability and we've all forgotten than our grandmothers and great-grandmothers took childhood illnesses very seriously. And so we combine rejecting the modern medical answers (vaccines and antibotics) with adopting the modern attitudes towards illness (NO big deal! Take them out in public!). I think that's a dangerous combination of attitudes.
I'd plan on keeping them home, if not for a full month, at least for the week that it says its very communicable, and preferably a week after that.
I'd certainly not take them out for a completely unneccessary event like a street festival. There are sometimes things you need to do -- go to the doctor, pick up prescriptions or supplies. But going to the fair? Nope.