The SARS-CoV-2 virus typically enters the body by attaching itself to a structure on the surface of our nasal membranes. This is the protein ACE2.
Once inside the body, the virus moves around by attaching to the same ACE2 protein on other tissues deep in the lungs, the heart, and the kidneys. The receptor can also be found in the lining of blood vessels, and possibly even the taste buds on our tongues. This is one reason why Covid-19 patients may present such a diverse set of symptoms.
A paper recently published in JAMA examines one measure of the amount of receptors in the noses of children and adults. I say one measure because what is measured is not the protein responsible for attachment, but rather the RNA which directs its production. Usually but not always, the amount of RNA in cells determines the amount of the corresponding protein. The authors assume that is the case, and their conclusion depends on that assumption.
With that caveat in mind, they report finding less ACE2 RNA in cells scraped from the noses of children than in those from adults. Participants in the study were divided into four age groups: less than ten, 10-17, 18-24, and older than 24.