The Generation R Study Group, Erasmus University Medical Center, PO Box 2040, 3000 CA, Rotterdam, The Netherlands. Department of Pediatric Oncology, Hematology and Immunology, University Medical Center Heidelberg, Heidelberg, Germany. ISGlobal, Barcelona, Spain. Universitat Pompeu Fabra (UPF), Barcelona, Spain. CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain. Department of Pediatrics, Sophia's Children's Hospital, Erasmus MC, University Medical Center Rotterdam, Rotterdam, the Netherlands. MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK. Bristol Medical School Population Health Sciences, University of Bristol, Bristol, UK. College of Life and Environmental Sciences, Psychology, University of Exeter, Exeter, UK. IMIM (Hospital del Mar Medical Research Institute), Barcelona, Spain. School of Oral and Dental Sciences, University of Bristol, Bristol, UK. Institut d'Investigació Sanitària Pere Virgili, Hospital Universitari Sant Joan de Reus, Reus, Spain. The Generation R Study Group, Erasmus University Medical Center, PO Box 2040, 3000 CA, Rotterdam, The Netherlands. j.felix@erasmusmc.nl. Department of Pediatrics, Sophia's Children's Hospital, Erasmus MC, University Medical Center Rotterdam, Rotterdam, the Netherlands. j.felix@erasmusmc.nl.