100%.
I learned about this in my biostatistics course. Specifically, poorer children were more resistant, on average, than wealthier children to polio because of their increased exposure.
The immune system, like everything else in your body, needs to be used otherwise it atrophies. Trying to hide from germs, to isolate yourself, only ensures that your immunity will weaken over time. It's also futile, since germs evolved to be largely inescapable. If we could actually hide from germs, they would've gone extinct a long time ago.