Do dogs eat their puppies while whelping?
Yes, in fact they can. It's rare, but sometime a "maiden" dog will not recognize her young as they are being born. Also, the dam will have a strong instinct to chew more than normal on the umbilical cord. This can result in the dam chewing on the legs of the puppy. In very rare cases the dam can continue on and eat the puppy. Dams who have undergone a C-section, who are also maidens, will not relate to the puppies for about 24 hours, they may very well want to kill them. Part of the reason for this is the anesthesia and the disorientation that results from it. This is seen much more in Terriers and other dogs with a strong prey drive.
When I help whelp a litter, I take the puppy as it is being born and break the sac and tie off the umbilical cord. I dry off the pup with a small, rough towel to stimulate it. Once it's viable, I place it in a shoebox lined with a towel and lay a thin towel over the box. I do not let the dam have the puppies until they are all born and things have settled down.
Do not let any other dogs in the area while whelping a litter, nor after the pups are born. Other dogs in the household may very well kill the puppies, too. This is not as much of an issue once they are over two weeks old.