No camera? No problem.
Animoto makes really professional looking videos from your pictures and video clips. You can choose from different templates for different looks, and insert written text.
http://animoto.com/
Photo Peach is another slideshow program, easy enough for children to use.
http://photopeach.com/
Zimmer Twins lets you make simple animated video stories.
http://www.zimmertwins.com/
Xtra Normal lets you create animated, narrated movies by typing in dialogue and dragging and dropping characters and set elements.
http://www.xtranormal.com/