“Big Buck Bunny” is a cartoon that you really should show to your students.
It was created by a professional team, using the free, open source tool Blender.
At the Web site, you can download the cartoon in several formats, or go to YouTube.
Then you should make plans to get your students involved in making their own cartoons. Maybe Blender will be too much to start for them, but consider using simpler tools. You can always have kids use TuxPaint, of course.
You can also start by doing storyboard frames on a piece of paper. Let your students concentrate on the story, using simple stick figures as the characters. Don’t rush them into worrying about drawing skills before they work out something to say. (Of course, they will want to rush.) Try out the template for a six panel page [Open Office Format].cartoon-panels
Then let students work with like Impress, the presentation tool of Open Office. There, with the drawing tools, have your students make a multi-page cartoon presentation shown as a sequence of frames, stepping through the presentation. Let your imagination be your guide.
Moving to Open Source Software in Schools 