To animate I usually use either Adobe Image Ready or Microsoft Gif animator. I have just been playing around with GoAnimate (another free Web 2 tool) and looking at the possibilities of using this tool in the classroom. It is very easy and children will love it. I can see a lot of ways making these animations fits into the Language curriculum but of course (with some lateral thought) they could make them around Social Studies, Maths or any other curriculum area.
I am going to use this tool with my students next year but would be interested to hear from anyone who has used it in their classroom.