“The idea that children either don’t get Covid-19 or have really mild disease is an oversimplification,” said Dr. Adam Ratner, the director of pediatric infectious diseases at New York University School of Medicine and Hassenfeld Children’s Hospital at N.Y.U. Langone Health. It’s true — and comforting — that there have been fewer cases detected in children, and that the case fatality rate is much lower in children than in adults, especially older adults, he said, but “we have had some extremely sick children.”

A study just published in the journal JAMA Pediatrics looked at 48 children in the United States who have required intensive care with Covid-19. Among other findings, 40 of them had significant medical issues, so-called comorbidities; half of these were categorized as “medically complex,” meaning they were dependent on technological support to begin with, as would be true of a child with a tracheostomy, for example. Other comorbidities included immunosuppression, usually connected to cancer treatment, obesity or diabetes.