Sean O’Leary, a pediatrician and a professor at the University of Colorado [School of Medicine], told me that families that include both kids under 12 and people who can’t be vaccinated or are at high risk for severe COVID-19 might want to be extra mindful of their kids’ exposure, because they could pass it to someone who’s not protected. He also cautioned that “we don’t really have good data yet” on how severe the Delta variant of the coronavirus, which is on track to quickly become dominant in the U.S., is in children, though it does seem to be more transmissible among people of all ages.