Parents and caretakers today have an aversion to letting kids get dirty, in part because of the notion that children may get sick from germs they pick up. Sadly, children spend half as much time outside as they did only 20 years ago.
For millions of years, children grew up in constant exposure to the microbes around them. Consider a child’s normal behavior from the start: babies continually put their hands, feet, and every imaginable object in their mouths. Older kids love digging in the dirt, picking up worms, rolling on the ground, catching frogs and snakes, etc. This natural behavior is likely designed to encounter more microbes and subsequently train their immune system to react to it accordingly.