What can cause liver cancer in a 5 year old child? isn't that very young?

Hepatoblastoma.: Hepatoblastoma is a malignant liver neoplasm in infants and children and composed of tissue resembling fetal or mature liver cells or bile ducts. Incidence is 1 in 1.5 million. It usually presents with abdominal mass. This is most commonly diagnosed up to age 3. Alpha-fetoprotein (AFP) commonly is elevated, but if not, prognosis is bad. Surgery, chemotherapy and transplant can be effective.

Hepatoblastoma: Liver cancers are very rare in kids (<2 cases per million annually), but they do happen. Most common form is hepatoblastoma, followed by hepatocellular carcinoma. Inherited syndromes are thought to be the main risk factors for the development of liver cancer in childhood. Parents' exposures are not clearly defined.