I've seen a few mother dogs eat their babies poop but not all dogs eat their puppies poop.
Although the mother dog will clean the puppies private areas with their mouths and tongue but not all mother dogs will actually eat the puppies poop when they poop on the ground.
However I have seen a few mother dogs eat the puppies poop and I've seen a few other mother dogs not eat the puppies poop.
So it can all depend on the mother dog as to whether they eat the puppies poop or not but it's not harmful if they do.