As a breeder of small dogs, after they are weaned, 1/2 puppy 1/2 adult food.
High quality food is a must.
By the time pups are 3 month-4 months old, slowly switched to adult food.
I don't know one breeder of small dogs that raises or keeps their pups on puppy food. Safer to have the pups on a high quality adult food, because of the risks of the very high proteins in puppy foods, that effect growth plates and rapid growth which should be avoided.