In 2001 the British Film Institute surveyed kids on their favorite cartoons and cartoon characters.  Here are the results.

Five essential ingredients for successful animated characters:

1. They should make children laugh or feel happy – with their different looks, funny voices, use of imitable catchphrases;
2. They should expand children’s imaginations by blurring fantasy and reality – by doing things real people cannot do or acting irreverently;
3. They should remain in character and behave logically, however fantastic their situation or location;
4. They should have a problem to solve, go through a journey or adventure – but their stories need not always end in the same predictable, entirely successful outcome;
5. They should have natural movements and their mouths should form words properly – children have high expectations!

The type or style of animation – whether characters are drawings, puppets or models – is not so important; neither is the country of origin.

Further details here.