Exchange bodily fluids with as many young people as possible. AFAIK there’s no way to be able to get voluntary exposure in a lab. Which is lame, imagine getting a precise dose of cultured $HCOV.

OC43 has like a 9% nursing home fatality rate tho (which is kind of a hint that SARS-2 isn’t too special as far as mortality is concerned)

Anyway if you have kids you have probably already been exposed to one of these CoVs at some point. The TL;DR is the more you do real life stuff the more likely you are to have exposure. Add it to the long list of externalities due to lockdown. Natural spread of pathogens is a good thing and not to be feared.