One of the most common causes of liver damage in children is extrahepatic biliary atresia (EHBA). In this condition,  the biliary of the liver is damaged since birth due to bile accumulation in the liver. 
If prolonged, it leads to the liver suffering from cirrhosis. This gradually and eventually leads to the child  having liver failure. EHBA causes  60% of liver failure  in children. This condition occurs in 1/15,000 children.
The other reason of liver disease in children are the metabolic defects of the liver, which occur due to defects in enzymes that are processed in the liver. In that case, the metabolic cycle by which toxic substances are cleared and the nutrients are absorbed,  begin to malfunction. This causes  abnormal products to deposit in the liver causing liver damage and cirrhosis. 
Also read:

Air pollution increases the risk of miscarriages to a great extent

4 Harmful effects of getting a Tattoo