Site or program for teaching flash?

I know this seems like a strange question for a Scratch message board but I didn't know where else to ask. I've been teaching Scratch this summer to teach game design but I also want to give my kids some exposure to flash game design as well. Does anyone know of a good online or offline application to teach flash? I need something that is free or cheap (preferably free). I need something that kids could learn.

Thanks!