Vitamin D2 vs Vitamin D2 Plus Calcitriol in Cholestatic Children With Vitamin D Deficiency

The goal of this clinical trial is to learn whether adding calcitriol to vitamin D2 can improve vitamin D deficiency in children with cholestasis and chronic liver disease. Cholestasis is a condition in which bile flow is reduced, which can make it difficult for the body to absorb and process vitamin D. The study will also learn about the safety of using vitamin D2 together with calcitriol. The main questions it aims to answer are: * Does vitamin D2 plus calcitriol increase blood 25-hydroxyvitamin D (25-OHD) levels more than vitamin D2 alone after 3 months of treatment? * Does vitamin D2 plus calcitriol help more children reach an adequate vitamin D level by 3 and 6 months? * What medical problems, especially high calcium or high phosphorus levels, occur during treatment? Researchers will compare children who receive vitamin D2 alone with children who receive vitamin D2 plus calcitriol to see which treatment improves vitamin D levels more effectively and safely. Participants will: * Take vitamin D2 alone or vitamin D2 plus calcitriol as assigned by randomization * Visit the clinic for study assessments at the start of the study, at 3 months, and at 6 months * Have blood tests to measure vitamin D levels, calcium, phosphorus, parathyroid hormone, liver function, and other safety markers * Have their treatment reviewed at 3 months; participants whose vitamin D level remains low may have their treatment adjusted according to the study plan * Bring back medication packages so researchers can check how regularly the study medicines were taken