A team of pediatricians from The University of Texas Health Science Center (UTHealth) and Baylor College of Medicine (both TX, USA) have published in American Journal of Physiology-Lung Cellular and Molecular Physiology the data regarding how differences in lung physiology and immune function in children may explain why they avoid severe COVID-19 compared with adults.
https://journals.physiology.org/doi/full/10.1152/ajplung.00183.2020