Six thousand U.S. parents and kids are doing DIY nasal swabs twice a week to answer some of the most vexing mysteries about the coronavirus. They're enrolled in an experiment investigating how many children are infected, how many have symptoms and how likely they are to spread it. The answers could help determine the safety of in-class education during the pandemic. But results aren't expected before the end of the year. Evidence from the U.S., China and Europe shows children are less likely to become infected with the virus than adults. They are also less likely to become seriously ill when they do get sick.