This movie maker is short, simple and quick or sweet.... One of the better one.It's called Dvolver at http://www.dfilm.com/live/moviemaker.html and you select what you want, what backgground, what action ext, but the load up time is fast. The only problem is it's a little too adult for elementary. Take a look and test this alone before you give this one to kids.
See below for the sample.... It took me less then 2 minutes to make this short scene.