Puppies, before becoming successful adults, have to go through several stages.
From their birth to 2 weeks
Newborns are blind and deaf (they open their eyes only fifteenth day after their birth). They are totally dependent on their mother and their activities are only to suckle and sleep. Nevertheless, they are very sensitive to the external environment.
Between 2 and 4 weeks
Puppies begin to see and hear, as well as to move. They discover the world around them and their bodies. This is the perfect time to establish contact between them and humans, through delicate manipulations.
From 4 weeks to 5 months
It is an important time for the puppies since it is the socialization period. They learn canine hierarchy and become more and more independent, especially with their owners. This is the perfect moment to teach them the rules of life such as meal times, sleep, etc.
They will then learn to obey and stay clean and then, once the vaccines are up to date, they will be able to discover new external stimuli and also meet their peers.
From 5 months to 1 year
The mother would end up one day or another repelling her puppies. This period of detachment, which is very important, is often interrupted by the puppy adoptive family who recreate an emotional universe around them. This explains their important attachment to their owners, which sometimes causes desperate actions, such as the destruction of furniture or barking when they are absent.
Dr. F. Savary