A Study to Evaluate the Dose-exposure, Safety, and Exploratory Efficacy of Nerandomilast in Children and Adolescents From 2 Years to Less Than 18 Years of Age With Fibrosing Interstitial Lung Disease (Part A: Double-blind, Placebo-controlled in Children From 6 to Less Than 18 Years of Age and Open-label Active Treatment in Children From 2 to Less Than 6 Years of Age), Followed by an Open-label Phase With Active Treatment (Part B)

This study is open to children and adolescents aged 2 to 17 years with interstitial lung disease (ILD). Nerandomilast has just been approved in some countries to help adults with a lung condition called idiopathic pulmonary fibrosis. The purpose of this study is to understand how nerandomilast is tolerated and handled by the body and whether nerandomilast also helps children and adolescents with ILD. For participants aged 6 to 17 years when joining, the study has 2 parts. In the first part, participants are put into 1 of 2 groups randomly, which means by chance. One group gets nerandomilast and the other group placebo. Placebo looks like nerandomilast but does not contain any medicine. Participants are twice as likely to be in the nerandomilast group. They take tablets twice a day for 6 months. After these 6 months, in the second part of this study, they get nerandomilast for at least 2 years regardless of what they got in the first part. Young participants aged 2 to 5 years when joining get nerandomilast from the start. They receive tablets twice a day for at least 2 and a half years. Depending on when a person joins, the study lasts between 2 and a half years and up to 5 years. During this time, participants may visit the study site about 18 to 30 times. Study doctors collect blood samples to check participants' health and to find out how their body handles the study medicine. Doctors also check the function of the lungs, body growth, and how participants feel. The study doctors also regularly check participants' health and take note of any changes. For participants aged 6 to 17 years, the results are compared between the groups to see whether nerandomilast treatment helps children and adolescents.