Ideally, nursing should slowly reduce after the first three to four weeks. Puppies are very tender creatures, and if they are not given proper care, they may also develop some permanent issues like malnutrition and lousy digestion. It is necessary that you let your dog feed for 3 to 4 weeks only on mother's milk and don't feed them any extra food. As they grow, you can start by adding tiny doses of hard food materials to their diet. You can boil them or soften them or mix some puppy food for your younger dogs to make them independent and give them proper nutrients for their growth.