Traditional forms of animation are filmed as stop-motion where the camera is stopped and the subject moved and then filmed again. This sequence of shots with small changes in between is linked together to create a moving image.
2-D animations have, or appear to have the physical dimensions of height and width, but are flat on the screen with no depth. 2-D forms of animation include model animation, claymation, pixilation animation, cut out animation, and drawn animation.
3-D animation is a newer form of digital based animation where the subjects can be viewed from all sides and the camera can move though the setting creating a more realistic sense of depth. 3-D animation uses the dimensions of height, width and depth.
Film Education (UK) has an excellent Primary Animation Resource.
MakeMovies offers a wealth of information about all aspects of animation production.
3D animation software
Moviestorm has an education version available for schools. It is available for both Mac and Windows platforms.
Muvizu is free 3D animation software available for Windows only.