**Core Concept**
The question is testing the knowledge of the most common type of hematological malignancy in children, which involves the study of pediatric oncology and the epidemiology of blood cancers.

**Why the Correct Answer is Right**
Acute Lymphoblastic Leukemia (ALL) is the most common type of leukemia in children, accounting for approximately 80-90% of all childhood leukemia cases. It is a type of cancer that affects the blood and bone marrow, characterized by the uncontrolled growth and accumulation of immature lymphoid cells. The exact cause of ALL is unknown, but it is believed to result from a combination of genetic and environmental factors. The pathophysiology of ALL involves the disruption of normal lymphoid cell development and maturation, leading to the accumulation of malignant cells in the bone marrow and peripheral blood.

**Why Each Wrong Option is Incorrect**
**Option A:** Although Acute Myeloid Leukemia (AML) is also a type of leukemia, it is much less common in children than ALL.
**Option B:** Lymphoma is a type of cancer that affects the immune system, but it is not typically classified as a type of leukemia.
**Option C:** Chronic Myeloid Leukemia (CML) is a type of leukemia, but it is much more common in adults than children.

**Clinical Pearl / High-Yield Fact**
It is essential for pediatricians and oncologists to recognize the symptoms of ALL, including anemia, bleeding, and infection, which can occur due to the bone marrow's failure to produce normal blood cells.

**Correct Answer: C. Acute Lymphoblastic Leukemia (ALL).**