Is your 9 year old anorexic?

Yes. If such is suspected, consult a health care practitioner.

---New Answer: Ranging from any age, people can have eating disorders.

Theres a chemical that tells your body when to eat, and when not eat. If that chemical goes out of control, the child or say, person, can become overweight. Even if they don't eat much, the chemical can tell the person's body to store the food as fat.