According to the New England Journal of Medicine, early exposure to potentially pathogenic organisms in life causes an individual to have a more robust immune system and less allergies. This is due to the activation of certain T-helper cells and the release of cytokines which activate macrophages and other innate immune cells. Shelter from these exposures could be detrimental to the child's health when they become adults. Because of the lack of exposure to potential pathogens and allergens as well, children who live in a sterile or supposedly sterile environment will be more susceptible to autoimmune diseases, allergies, hypersensitivities and be more sickly in general.

What does this all mean?
I'm taking my kids to Yosemite every year and having them play in the water and the meadows. AND, to the park/beach weekly. None of this stay at home and be clean all day. Besides, i like going outside.