Infection with at least some of those "common cold" human coronaviruses seems to have much the same effects on kids and the elderly (and maybe everyone else too

Infection with at least some of those "common cold" human coronaviruses seems to have much the same effects on kids and the elderly (and maybe everyone else too) as Covid-19. At least part of the reason we're not seeing a huge pandemic of those is that lots of people already have immunity, but that also makes infecting people with them less useful - the people who already have immunity to those aren't likely to develop new immunity, and the people who don't presumably won't necessarily develop immunity that crosses over to Covid-19. (Unfortunately, since common cold research is a lot less big, glamourous and high-profile than Covid-19, I don't think we know a huge amount for sure about the other human coronaviruses - and what we do know isn't exactly front-page headline news.)