> "People who grow up on farms are generally less likely to develop asthma, allergies, or auto-immune disorders like Crohn's disease – thanks, apparently, to their childhood exposure to a more diverse range of organisms in the rural environment that had encouraged more effective regulation of the immune system."
The vast majority of farming in the USA and Britain is industrialized and relies heavily on regular application of pesticides and herbicides in the fields. Animal farming is centered on factory farms where animals are kept in close quarters and given antibiotics and hormones to prevent disease outbreaks and increase growth rates. The fecese and urine from these operations stink for miles around.
Childhood exposure to such environments results in everything from asthma to neurological damage - see Parkinsons relationship to organophosphorous pesticides, say. Another concrete example: methyl bromide in the strawberry fields of California:
https://www.ewg.org/research/heavy-methyl-bromide-use-near-c...
That's the industrial agriculture reality, so packing your kids off to such farms to get their dose of 'good natural microbes' is inadvisable. It's just half the equation, however, as other kinds of industrial activity have loaded up soils with all kinds of chemical contaminants, from heavy metals (sometimes radioactive) to persistent organics with negative health effects. For example, anyone living downwind of an oil refinery or coal power plant, or around a uranium mine etc., should thing twice about galavanting through the local mudholes. Richmond, in California downwind from Chevron and other refineries, is a case example:
https://www.ehn.org/pollution-poverty-richmond-2645503359.ht...
Even without the modern industrial-related issues, historically animal farming has been linked to all kinds of parasite issues, such as the hookworm pandemic that afflicted the American South for many decades (linked to pig farms). The 'get in touch with nature on a nice organic farm' theme should be tempered by such realities, i.e.:
https://www.pbs.org/wgbh/nova/article/how-a-worm-gave-the-so...
However, direct interactions with relatively pristine natural environments are likely great for kids (and adults), and the notion that ultra-sterile equals ultra-healthy doesn't make any sense either.