I would review the marketing tools on
http://usfirst.org.
Link here:
Marketing Tools
There are also a few videos that are exciting to show the students:
Official FIRST YouTube account
What is FRC?
Other ideas:
Have students draw pictures of what they think a robot looks like.
After, show them pictures of FRC robots and robots in the real world.
Have them compare their pictures with the real pictures and explain what they learned just from looking at the images.
Have students write what they think an engineer and scientist does.
After, have them research actual engineering and scientist specific jobs.
Have them compare their writings with the research they did.
Have them do a KWL activity:
Knowledge already: Students write down what they know about robotics, engineering, STEM, etc.
What you want to learn: Students write down questions they have about those topics.
Learned: Students answer each others questions, the people managing the demo can answer their questions, or students can research answers to their questions in order to "Learn" more about it.