Should 3 week old puppies eat dog food?

At 3 weeks of age, they are old enough to start on soft mushy puppy food. I would soak the dry puppy food (use a good name brand puppy food) for a long time until very mushy, then add some evaporated canned milk, diluted one part milk to one part water. Do not use regular cow's milk as it is not good for the puppies & can cause diarrhea. Then you can add in a little bit of human baby rice cereal (helps to keep the pups' stools firm). Mix it up and it should be diluted enough that the pups can actually lap it up. They will make a mess at first but will lick it off of themselves. As time goes by, make is less and less watery and more just soft puppy food. If you see diarrhea, then add in more human baby rice cereal. Pretty soon just feed them the softened dry puppy food, then go to just dry only. Don't forget about deworming them at 4 weeks, 6 weeks and a final deworming at 8 weeks. Also vaccinations too. The pups should all have a check up done by your Veterinarian.