As a traveler with numerous trips to India, and seeing the abject poverty displayed everywhere throughout my travels, a child does not survive without developing an incredible immune system. The filth that is EVERY WHERE is mind numbing. Every morning I soaked a t-shirt to make a mask so I could breath. Mumbai has no birds; the ones who fly in drop out of sky dead from the wretched air control. I’ve been to every major city spread across the country and found a clean area.
There's a lot to that. Whereas in this country, people are so germ-phobic, they don't let their kids play in dirt and they are obsessed with keeping their house clean. The immune system is like a muscle, use it or lose it.