I agree. If your student are using Windows, just ask them to use Windows Movie Maker. It'll most like have a lot more to offer than other, free, open source programs.
I know this is a bit off-topic for what you need, but if your students need to do audio and image edditting... Audacity (audio edditting) and GIMP (image edditting) would be perhaps the best open source softwares for them to use.