Jillybird From a paper in Nature: "Children’s ability to neutralize the virus might also be linked to the fact that they have a strong innate immune response from birth, says Alasdair Munro, who studies paediatric infectious diseases at University Hospital Southampton, UK. “There’s been some suggestion that the rapidity and scale of their innate immune response might be protective against the initiation of infection,” he says. But this effect is difficult to study, and raises the question of why it isn’t seen with other viruses that can cause severe disease in children, he says.
Other factors
Children are also the main reservoir for seasonal coronaviruses that cause the common cold. Some researchers have suggested that antibodies for these coronaviruses might confer some protection against SARS-CoV-2, but the evidence is mixed says Munro.
Meanwhile, there is evidence that when children are exposed to the virus, they receive a smaller dose than adults, because their noses contain fewer ACE2 receptors, which the virus uses to gain access to cells. This might also explain why COVID-19 is less prevalent in children than in adults, say researchers.
doi: doi.org/10.1038/d41586-020-03496-7