Mystery of the Silent Friends

This was one of my favorite books as a child. I read and re-read this so many times that the cover was gone. As I recall, the story involves mechanical dolls (the "silent friends") found in the protagonist's father's antique shop. Suddenly, two men appear at the store eager to buy them. Why, after they have sat in the store so long?
A pleasurable read for every child. Highly recommended.