Hello, this is Dr. Linda. I hope I can help with your question today.
I am sorry for your concerns about your Border Collie & her pups. If you have just noticed the diarrhea, but everyone seems happy & otherwise healthy, then I would definitely deworm Mom & the pups.
You can purchase a very safe wormer from any pet store or your vet without a prescription called pyrantal pamoate. Administer by mouth, 1 cc per 10 pounds of body weight. It is a very safe wormer, so your weights do not have to be exact. Repeat the wormer in everyone in 2 weeks, then 2 weeks after that.
This wormer does not get everything, but it will get the hookworms & roundworms that can really drag a pup down. If the stool does not firm up in several days, or if anyone quits eating &/or becomes lethargic, then you will need to take a fecal sample to your vet, or have them examined.
I hope this makes sense & you find the information helpful. Please let me know if you have any further questions or concerns.