What is different about Doodle?

The narrator's younger brother, real name William Armstrong. Doodle was born with a caul, or a membrane that sometimes surrounds the head of a child at birth. As a result, he has a number of developmental disabilities, and he is not able to walk until age five, when the narrator teaches him. Doodle is hopeful, energetic, and determined, with an eye for things that are beautiful.