My personal rule is that if fever is gone for 24 hours and everyone feels well, we go back to normalcy. If I were worried about my child being contagious, I'd bring anti-bacterial wipes and sprays and use as necessary. I'd warn people "ds was sick earlier this week, so no hugs and kisses today." I'd watch closely and make sure that no cups and utensils are shared. No touching babies (which is a good rule anyway).
If someone is immuno-compromised and going to the fair, I'm guessing they'll be taking care to avoid germs already.
2) My sister, who is immunocompromised, still has to: get in a busy shared elevator, take the bus to the train station, take the subway, and go to work, and then back. And yes, she sometimes likes to go, you know, to fun things out in public. In one of the biggest cities in the US, even.
Mostly she's fine other than more coughs and colds than most experience. But then sometimes people cross her path with things like, oh, pertussis, which she had this past winter, and now, possibly TB. I guess she should quit her prestigious job and stay home 24/7 to remain well, which would be super fun for her because she also has mild CP and relies on a wheelchair to get around, because sometimes people don't have common decency to stay home when they're sick.
I'm sorry, but this topic irks me to no end. The responsibility isn't on the person who is immunocompromised to make sure your knowingly sick kids don't make them ill, it's on you.