While the overall hospitalization rate was low compared to adults, nearly one third were admitted to the ICU and one child had died.
The highest hospitalization rate was among children who were younger than two years old, Hispanic or Black.
In the second study, researchers examined 540 reports of Multisystem Inflammatory Syndrome in Children, or MIS-C, from 40 states.
The average age was eight and more than half of the patients were boys, and 40% were Hispanic or Black.
Most cases included features of shock, gastrointestinal symptoms, significantly elevated markers of inflammation and damage to the heart.
All but five had tested positive for COVID-19, while the rest were around someone with the virus.
The majority of the kids developed the condition between two and four weeks after infection.