© The Author(s). A characteristic of the novel coronavirus disease 2019 (COVID-19) is the few cases of severely affected children. They not only rarely get symptoms but also seem to be poor transmitters. We propose that this may be explained by the mechanism of breath droplet formation, which occur during the re-opening of collapsed terminal bronchioles. Children's lungs are still developing. Compared to adults they have few alveoli and terminal bronchioles, thus less sites of aerosol formation where virus-loaded lung lining liquid can get airborne. In addition, children have a lower respiratory minute volume and tend to have a lower viral load. These points, together with the fact that asymptomatic carriers release less aerosols than symptomatic carriers support the idea that children are indeed poor transmitters of the COVID-19 virus.