Immune systems aren't like a muscle. You don't make them stronger by exposing them to a bunch of viruses. Often you can make an immune system weaker by infecting people with things like the flu that actively attack a person's immune system and their t-cells. This is why people seem to be catching more sicknesses and having more sick days than ever before... people's immune systems are absolutely demolished.
I absolutely think that getting good air filtration in schools, offices and public spaces would make people healthier in both the short-term and the long-term.
Exposure to germs and allergens almost definitely improves immune systems in later life.
This is more due to the lack of exposure over the last few years, as well as all the antibacterial, hand washing.
Perhaps in places where air quality is terrible, like overpopulated cities.
Sorry dude, I don't know how to say this... but your thinking here is way out of date.
Lack of exposure is a total myth, it's just not true. People are sicker now because Covid, RSV, Flu, etc etc attack the cells that fight off disease. You get sick once, you end up with less t-cells (the cells that fight viruses), so you get sick again in a couple of months... when normally the second one wouldn't have affected you.
If the lack of exposure theory was correct, wouldn't it have played out by now, 3 years later? If it was true, there would have been a huge spike after lockdowns, etc, and then people's immune systems would have gone back to normal... instead people seem to be constantly sick because of their weakened immune systems.
There is absolutely no advantage to getting sick.
The measures to avoid sickness, like good air filtration and hand washing, is what makes people healthier, not constantly catching colds and flu.
Here is an interesting talk about immune systems and allergens.
[The Peter Attia Drive] #277 ‒ Food allergies: causes, prevention, and treatment with immunotherapy | Kari Nadeau, M.D., Ph.D. #thePeterAttiaDrive https://podcastaddict.com/the-peter-attia-drive/episode/166035324 via @PodcastAddict
Though, I think you are missing the point of the article.
I totally understand the point of your post, and I hope you are able to take some time off work to spend some quality time with your daughter. I'm sure she'll remember your effort for years to come and it may even shape the way she looks after people when she grows up... so I think there's an amazing opportunity for you to teach her something special.
But also... if my thinking was the exact opposite of the way things work, I'd want someone to call it out too.
That podcast definitely seems really informative in treating food allergies... but obviously food and viruses are very different. Catching a cold virus when you're a kid doesn't prevent you from getting colds as an adult... I'm sure both you and I would have absolutely invincible immune systems and wouldn't have had a runny nose or sniffle in 35 years if that were true.
Colds and flu change over time, which is why we keep catching them. A yearly flu shot (it isn't a vaccine) is based on a prediction of what the future flu will look like, which means that sometimes it works, sometimes it doesn't, but what it is looking to do is try to mimic what is to come. However, the more robust and broad the antibody range is in a person, the better they are able to handle future flus. It is like having diversity, there is less single points of vulnerability, like a distributed network. My thinking isn't the exact opposite of the way things work.
For instance, if a kid gets chicken pox, they itch for a bit and a few days later they are fine. If an adult who has never had chicken pox before gets it, it can be very severe. Chicken pox is a virus.