As the first clinical trials in young children start, here’s what scientists want to know. Parents are clamouring to enrol their kids in the first COVID-19 vaccine trials in young children. “Somebody told me they called and called and called until they were allowed to participate,” says Kawsar Talaat, an infectious-disease physician and vaccine scientist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. She is part of a trial that began testing the Pfizer–BioNTech vaccine in children under 12 in late March. As such trials get under way — Moderna began a similar study of its...