Money is explained by this 1947 Coronet film.
It explains the progression of our economic system, beginning with bartering by early humans. Because of specialization, bartering is no longer appropriate and money has emerged. First there were spearheads and other unreliable forms of wealth, which eventually led to the use of silver and gold coins. The mint system is shown as it is explained that the government is the backbone to the value of our money.
Although it shows its age, as a 1940s film, it would spark some interesting discussions on money in any Social Studies class.
Social Studies and History Teacher's Blog 
I am a children’s author and video maker currently producing a new series for children titled MEET ME AT THE CORNER. This series of virtual field trips is being distributed over the Internet as video pod casts on our web site http://www.meetmeatthecorner.org
Directed at America’s school children, each show explores the world and its wonders from a child’s point of view. During each video pod cast a child host serves as tour guide, leading the viewer to historic and cultural sites. Each show includes a suggested reading list and a Learning Corner of follow-up activities for school children ages eight to twelve.
Take a look at the episode on the Money Museum, a Virtual Field Trip to Colorado Springs, Colorado
http://www.meetmeatthecorner.org/episodes/lincoln-penny-money-museum
All shows come with links to fun websites and a Learning Corner of questions and extended activities. New episodes are uploaded every two weeks.