The Minnesota Historical Society offers a fantastic video on the topic of primary v. secondary sources. By watching the short video students can learn what a makes a resource a primary or secondary source. The video provides a handful of examples of each along with a description of what makes the example a primary or secondary source. This is probably the best video that I have seen explain the differences between primary and secondary sources.
Using Primary & Secondary Sources is a video that was produced by the Oregon School Library Information System. The video is intended to help elementary school students understand the difference between primary and secondary sources. The video uses some clear examples of each type of source and how those sources can be used in the research and writing process. The best part is that there are examples aligned to multiple subject areas including art and science.