As the world passes the grim milestone of four million reported COVID-19 deaths, our study reveals that 2 million children at a minimum have been directly affected by this hidden pandemic. The overall numbers are shocking as well: through early July 2021 at least 1.5 million children lost a parent, and two million children lost a parent, grandparent or relative who lives with them and is involved in caring for them. We start with data on COVID or excess deaths, broken down by age and sex for 21 countries comprising almost 80 percent of worldwide COVID deaths. Whatever the true numbers, our study now reveals the hidden pandemic that accompanies them: if only another two million COVID deaths are reported in 2021, this will equate to another 600,000 children experiencing orphanhood and one million children experiencing the death of a parent, grandparent or caregiver. COVID can kill in a matter of days or weeks, giving families little time to prepare children for bereavement.