Parvo is distemper, which is preventable with vaccinations. Although the kittens can't be vaccinated until 6-8 weeks, if your other animals are all up to date on vaccinations, there will be little risk to them.
We lost Garfield's brother Odie to distemper, and he had a real bad case. Their Mom (Tigger) needed blood transfusions to survive. It is a horrible, mainly preventable illness. (About 10 days after they were turned into the rescue, Odie was gone, and Gar and Tigger were critically ill.)
If you get distemper with unvaccinated cats and kittens, it is very deadly. Remember, it can be tracked in on your shoes. We lost a dog to canine distemper...had friends over who lost a dog to horrible diarrhea several days before. Somehow, by them and their children visiting, our young dog caught distemper. A week after their visit, and about $1,000 later, our dog was dead. Had we kept up on his vaccinations, he would have been fine.