I heard eating poop in animals was a behavior and if one dog sees another doing it they will to. I don't think it is good idea to allow it not that you do....my new saint bernard likes eating chicken poop. I keep stopping her but for some reason they like to.
I though I heard one time that there is something in it they are lacking nutritionally?
I don't know what kind of a dog you have but it is very necessarily to have a good quality food just like it is for us to be healthy we need to eat healthy also for them to grow properly especially as puppies. Large breed dogs take 2 years for maximum bone development. They grow so fast it is like their bones are hollow and then get more solid after hence the 2 years and I am sure other parts of the body also.
I am sure chewing and eating everything is just puppy/dog board-em/behavior.
Good luck!