Besides the obvious kid as the main character of picture books, a quick perusal of my bookshelf this morning yielded a great array of other characters -- I'm sure you add to this list. Bee, llama, giraffe, hippo, unicorn, panda, cabbage, bundle, cowpoke, gorilla, bunny, dragon, serpent, pig, piggie, tater-tot, whale, fish, worm, puppet, dog, kitten, shark, starfish, chicken, cow, horse, lamb, alien, gator, cowboy, duck, troll, leprechaun, brother, sister, cousin, train, car, wagon, goose, cheetah, bean, egg, pea, sweet pea, otter, dinosaur, t-rex, lion, owl, goose, pumpkin, witch, ghost, pearl, clam, spider, banana, goblin, skeleton, longhorn, magician, sorcerer, wizard, hat, donkey, tree, dandelion, farm. What else?
