According to this study out of Australia and schools, they found children are not primary drivers of transmission. It doesn't make sense to me logically, but I am not an epidemiologist and I am not claiming this as fact, just interesting. I believe Sweden also is allowing children under 10 to visit grandparents as they also found low transmission from young children to adults, but not allowing visits from older children and teens.
COVID-19 inschools–theexperienceinNSW
ETA: maybe the youngest have the strongest immune systems and killing off the virus quickly , thus not spreading it. It's a theory. Like the opposite of H1N1.