To make convincing animation, you have to believe that the character is alive. It's more than movement, more than action. Animate comes from the Latin animari: to impart soul- a breathing, living, internal energy. The character has to appear to make its own decisions and to be behaving by its own motivation. To do this you have to pay attention to the natural world. There are three simple concepts to help children and others animate a character:
PATHS OF ACTION
1) Paths of action: with pauses, and acceleration and deceleration. This is traditionally called ease in/ ease out. In England it's called faring in and faring out.
2) Rotation: if a character does not have a lot of moving parts, you can bring it to life by rotating it, giving different perspective. This is simple movement. When you turn your head to look at a clock, the clock is rotating, but so is (partially) your head. If you combine path of action and rotation you have ice skaters, weasels, baton twirling, etc.
3) Configuration Change: metamorphosis. Change color, shape, size, or the makeup of the character. Lip synch uses metamorphosis, by replacing one mouth with another mouth.
Characters have attitude. Take Kermit the Frog. Kermit's only movement is to open his mouth and turn his head. But Kermit is convincing, because he does it with attitude, inflections, and timing. We all know Kermit as a living creature.
Some people don't ever shoot any stop motion without first shooting reference film (of real characters performing similar movement). If you use this film to guide your character movements, it is very effective at getting your timing right. But you need to amplify the expressions within the reference film by 2 or 3 times. You can get very smooth movement this way: ease in, accelerate, cover the distance, ease out.
An alternative form of movement, using the same number of frames, is to hold back, hold back, hold back, and then rush through the movement and then getting there with a more compressed ease out. This can be a much more dynamic move. Sometimes you can go past the destination point, and then snap back. It's the same jolt that a dog feels at the end of a chain. The dog is going full bore, and doesn't anticipate the stop until it snaps.
You can also show a little more internal motivation on the part of the character by using anticipation. Before the move, go in the opposite direction. It sets up the movement. It's Newton's law - every action has an equal and opposite reaction. Before a frog hops, it has to crouch down, before a pitcher pitches, he/she has to bring back the arm and then snap it forward. There has to be anticipation. Anticipation is the setup - it can be in the hips, in the feet, in the cock of a head, or the opening of a hand. It can be more complete too - the squeezing down of the entire skull, eyes squinting, teeth gnashing , the head getting smaller. Only hold it for one frame-- you don't want to freeze on that frame. Then the head explodes upwards and outwards. A huge expression. The eyes can then become as big as dinner plates. That's called a take. The big eyed, Tex Avery, Roger Rabbit, huge expression needs an anticipation, otherwise it looks like the character is inflated from some outside force. You need anticipation to show internal motivation, not external motivation.
Finally, characters breathe at the fingertips. It does you no good to build up the chest, inflate and deflate, unless you want to show exaggerated breathing, or snoring. The breathing, living gesture, which makes the character seem alive, happens with small inflections at the tapered tips: fingers, hair, tails, neck.