In contrast to the young narrator, the adults all have certain pre-conceived notions about the disabled William Armstrong, who is later called Doodle.
- Aunt Nicey, who acts a midwife, declares that the baby will live because he is born in a "caul," a gossamer-like membrane that, according to her, comes from Jesus's nightgown. This remark by Aunt Nicey characterizes her as one of those backward, country women who either create wives'-tales or help to preserve them. Remaining steadfast in her superstitions about a caul, Aunt Nicey disgrees with the others in their adoption of the name Doodle for William Armstrong when he survives infancy. When Doodle shows the adults that he can stand and walk, Aunt Nicey says a pray of thanks. She is religious, but in a fundamentalist, superstitious way. For instance, when the scarlet ibis dies, she says, "Dead birds is bad luck."
- Mama, who cries when she tells the narrator that his baby brother may not live, or, if he does, he may not be "all there," is pessimistic and despairing about her baby. When the two-year-old Doodle strains to turn himself, Mama, who believes the doctor's warnings that his frail heart may not take the strain, watches with great trepidation. Nevertheless, she loves the boy in a pitying sort of way, and demands that the narrator take his brother wherever he goes so that the child will have experiences of living. Always worried about Doodle, she cautions him not to touch the dead bird when the scarlet ibis lands.
- Daddy, who has the carpenter, Mr. Heath, build a small mahogany coffin for the baby, is a fatalist. He decides upon a name for the baby that would go well on a tombstone. When the baby does not die, he stores the coffin rather than throwing it away. As a cotton farmer, Daddy is familiar with the power of nature and, therefore, does not question it or try to defeat it as Brother does. He remains passive, accepting whatever fate brings him; however, when Doodle is older, the father builds a cart for Brother to pull him wherever they go. When the scarlet ibis appears, Daddy looks the species up in his book and tells Brother that the bird must have been brought by a storm, for it is out of place in their environment, indicating that his interest in the bird ends there.
Mama seems like a loving, very serious person who is intensely distressed by Doodle's condition.
Daddy is a cotton farmer, and he seems kind, loving, and even more serious than Mama almost to the point of being grave.
True to her name, Aunt Nicey seems like a nice lady and extremely religious.