The mortality rate in children would leave us with something like 10k dead kids country-wide if the virus is permitted to spread to everyone.
Mortality isn't the only issue, either. We're seeing plenty of signs some folks survive, but with long-term health impacts.
(An overwhelmed medical system will kill vulnerable kids in non-COVID ways, too. Mortality of things like car accidents and asthma attacks and suicide go up if the ICUs are full.)