http://vetmedicine.about.com/od/dise...t/a/CW-FIP.htm
following copied from above link
The coronavirus is spread through direct contact via the nose and mouth with infected feces, so sharing litter boxes is a major route of transmission of coronavirus. However, as previously noted, FIP only develops in some cats who are infected with the coronavirus, so exposure does not automatically mean cats will get FIP.


http://www.veterinarypartner.com/Content.plx?A=681 ***this link has some useful information****
following copied from above link
How Can an Infectious Disease not be Contagious?

Feline infectious peritonitis is a reaction to infection with the feline enteric coronavirus. Most cats who become infected with the feline enteric coronavirus (often simply called feline coronavirus) essentially get the flu and never develop anything that can in any way be described as serious. Some cats, however, react with this devastating syndrome.

I hope these links helps some.
praying its not FIP
You and your babies are in my thoughts and prayer.