Step 1: Indications for liver transplantation in infants and children include acute liver failure, chronic liver failure with intractable pruritus, complications of cholestasis and failure to thrive. Step 2: Among these, the single most common underlying disease in young children is biliary atresia, a progressive obliteration of the bile ducts that leads to cholestasis and cirrhosis early in life. Step 3: So option (a) Biliary atresia is correct. Step 4: Cirrhosis, hepatitis and drug reactions can cause liver failure too, but they are not the leading paediatric indication, so they are excluded.