Very sorry to hear that. How are the pups doing now? Did the vet diagnose it? If not, sometimes it can be other things, such as intestinal parasites, like coccidia.
Also, whenever you have pups that are very young and have just received their first vaccines, it's still a good idea to be extra careful with other factors, such as allowing visitors to the yard walk around their area, and pet them, etc. It may be friends coming over, but you never know where they walked through that could have possibly been contaminated, and next thing you know the virus is brought to your yard and you don't even know it. I'm not fully comfortable until they've at least had 2-3 of their vaccines. We also happen to keep a closed yard so we haven't ever had any issues thank goodness. We have had coccida pop up once though! We now add Sulmet in all the dogs' water pails. Darn free range fowl pooing everywhere.