Coronaviruses are part of the family of rhabdoviruses. The rhabdovirus family includes several viruses for which we already have vaccines or treatment. The list of viruses in the rhabdoviruses family explains why children are having none or less symptoms with coronaviruses—they were vaccinated more recently for related or similar viruses, to wit: MMR, polio, rotovirus, and influenza.
Rhabdoviruses include: coronaviruses–Crimean-Congo hemorrhagic fever orthonairovirus–Dengue virus–Ebolavirus–hantaviruses–Hepatitis B virus–human immunodeficiency viruses–Human orthopneumovirus–influenza viruses–Japanese encephalitis virus–Lassa mammarenavirus–Measles morbillivirus–Mumps orthorubulavirus–Norovirus–Poliovirus–Rabies lyssavirus–Rhinoviruses–Rift Valley fever phlebovirus–Rotavirus–Rubella virus–Tick-borne encephalitis virus–West Nile virus–Yellow fever virus–Zika virus
Here is an article showing encouraging new out-of-the-box thinking on a vaccine for coronaviruses, starting with a rabies vaccine.
https://www.youtube.com/watch?v=WbG6mzYUnyU&feature=youtu.be&fbclid=IwAR07cSRiUzBpr1LyW6_XXDtifWuQI9z0N3RTdP37Hv9HXv6oyu1qvRAe1gg