**Core Concept**
Iron deficiency anemia in children can be caused by chronic blood loss, which is often due to intestinal parasitic infestations. Hookworm infestation leads to chronic blood loss in the intestines due to the attachment of the worm to the mucosal lining, resulting in iron deficiency anemia.

**Why the Correct Answer is Right**
Hookworm infestation (Ancylostoma duodenale or Necator americanus) is characterized by the attachment of the worm to the intestinal mucosa, leading to chronic blood loss. The adult hookworms attach to the intestinal wall, causing damage to the mucosa and subsequent blood loss. This chronic blood loss leads to iron deficiency anemia in children, as the body's iron stores are depleted due to the continuous loss of iron-rich blood.

**Why Each Wrong Option is Incorrect**
**Option A:** Whipworm (Trichuris trichiura) infestation is associated with weight loss, abdominal pain, and diarrhea, but it is not typically linked to iron deficiency anemia.
**Option C:** Roundworm (Ascaris lumbricoides) infestation can cause intestinal obstruction, but it does not directly lead to iron deficiency anemia.
**Option D:** Pinworm (Enterobius vermicularis) infestation is typically asymptomatic and causes anal itching, but it is not associated with iron deficiency anemia.

**Clinical Pearl / High-Yield Fact**
In areas where hookworm infestation is common, it is essential to consider this diagnosis in children presenting with iron deficiency anemia, especially if they have a history of frequent blood transfusions or have not responded to iron supplementation.

**✓ Correct Answer: B. Hookworm. Hookworm infestation is associated with iron deficiency anemia due to chronic blood loss.**