Exactly. For example, look at a flower or a vegetable grown in a hothouse. Impressive looks-wise, but if you put it out in the backyard, it will die almost immediately because it’s been kept all of its “life” in isolation and not exposed to the open air so as to build immunity to diseases and garden pests.
Same principle applies regarding people.
Yes!!!
I have my mom’s Baby book from 1932. They common practice was “airing” the baby every day, even in winter - just opening a window for a bit. Michigan !!!