xxv Conflicts of interest Tobias Ankermann reports lecture fees from AbbVie, Allergopharma, Chiesi, Infectopharm, Novartis and Nutricia, and personal fees from Allergopharma for a safety board of a paediatric allergen specific immunotherapy study, all outside the submitted work. Laura Berdah reports support by grants from the Institut National de la Santé et la Recherche Médicale (INSERM), the Legs Poix from the Chancellerie des Universités, Paris (grants 2013 no. 1305, 2014 no. 1405, 2015 no. 1015, 2016 no. 2077 and 2017 no. DP2017/1860), the European Union’s Seventh Framework Program (FP7-ChILD-EU 2007-2013) under grant agreement no. 305653, as well as funding from the patient organisations Respirer c’est Grandir and Belleherbe Association. The ILD cohort was developed in collaboration with the Rare Cohort Disease (RaDiCo)-ILD project (ANR- 10-COHO-0003), the FP7-305653-child-EU project and the COST Action European network for translational research in children’s and adult interstitial lung disease (COST-ILD) project (CA16125). Jayesh Mahendra Bhatt reports lecture fees for an international educational meeting organised by Vertex Pharmaceuticals, outside the submitted work. Andrew Bush is an emeritus NIHR Senior Investigator and is funded by the Asthma UK Centres for Applied Research and the Centre for Allergic Mechanisms in Asthma. Anne B. Chang reports multiple grants relating to cough, bronchiectasis and PBB from the National Health and Medical Research Council (NHMRC, Australia), a grant from the NHMRC Centre for Research Excellence in Lung Health of Aboriginal and Torres Strait Islander Children (APP1040830), and an NHMRC Practitioner Fellowship (APP1058213), all related to the submitted work as well as support from GSK for being a member of a data monitoring committee relating to an unlicensed vaccine, support from Up to Date for being an author of sections on paediatric chronic cough, support for being an author of the chronic cough guidelines for the American College of Chest Physicians, and support (to her institution) from the BMJ Evidence Centre for being an author of two chapters on paediatric asthma, all outside the submitted work. Annick Clement reports support by grants from the Institut National de la Santé et la Recherche Médicale (INSERM), the Legs Poix from the Chancellerie des Universités, Paris (grants 2013 no. 1305, 2014 no. 1405, 2015 no. 1015, 2016 no. 2077 and 2017 no. DP2017/1860), the European Union’s Seventh Framework Program (FP7-ChILD-EU 2007-2013) under grant agreement no. 305653, as well as funding from the patient organisations Respirer