You should have a stool sample done they will have to have it sent out, need to check for coccidia and another parasite puppies can get is giardia so have it checked for that both of those things cause diarrhea and wormer will not help those so its important you know what you are dealing with so you can do some extra cleaning to keep from being re infected coccidia is very common in puppies. Both of these things will cause weight loss and severe diarrhea very bad things for puppies.
Puppies can be born with round worms but I would never deworm prior to 2 weeks of age. Usually diarrhea that young is caused from over eating or being given a supplemental formula. Since you are a breeder and have not yet messaged the Moderator Team, you may not discuss anything related to you puppies.
Please message me so I can see about approving you on the forum. In the mean time your thread will be closed as will any other questions in regards to breeding and your puppies.