One of the reasons (plausibly there are multiple reasons) for that may have to do with children having fewer ACE2 enzymes lining the nasal cavity: From May: ht

One of the reasons (plausibly there are multiple reasons) for that may have to do with children having fewer ACE2 enzymes lining the nasal cavity: From May: https://jamanetwork.com/journals/jama/fullarticle/2766522 https://jamanetwork.com/journals/jama/fullarticle/2766522 "The authors evaluated gene expression in nasal epithelial samples collected as part of a study involving patients with asthma from 2015 to 2018. The nasal epithelium is one of the first sites of infection with SARS-CoV-2, and the investigators probed for the expression of the cell surface enzyme angiotensin-converting enzyme 2 (ACE2), which has been proven to bind to SARS-CoV-2 spike protein and promote internalization of the virus into human cells. Among a cohort of 305 patients aged 4 to 60 years, older children (10-17 years old; n = 185), young adults (18-24 years old; n = 46), and adults (≥25 years old; n = 29) all had higher expression of ACE2 in the nasal epithelium compared with younger children (4-9 years old; n = 45), and ACE2 expression was higher with each subsequent age group after adjusting for sex and asthma."