Additional Study Information: The purpose of this study is to see how effective and safe the drug maralixibat is when compared to placebo in infants with biliary atresia who have had Kasai surgery within 3 weeks before participation. This is a 26-week, multicenter, double-blind, placebo-controlled, randomized parallel-group study, followed by an open-label extension (OLE). Approximately 3 subjects will be enrolled at CUMC. during part 1 of the study, participants will be randomly assigned to take either maralixibat or a placebo in an oral solution twice a day for 6 months. During Part 2 of the study, all participants will receive the study drug. Subjects will be expected to come to the study site for 11 to 15 visits during Part 1. For Part 2, subjects come to the study site weekly for the first 3 visits and then at least every second week for the next 5 weeks of Part 2. After that, study visits will take place once every 12 weeks. During these, visits the research staff will ask about the subject's medical history, check the subject's vital signs, measure subjects, perform an ECG, assess the subject's liver in a procedure called liver elastography, and collect a blood sample.