It appears that children not getting sick in the first few years of their lives paired with some mutations that aren't uncommon can cause the immune system to s

It appears that children not getting sick in the first few years of their lives paired with some mutations that aren't uncommon can cause the immune system to stay too weak. This is one of the leading theories why so many children get Leukemia. This is a pretty serious scientific study on the phenomenon: https://www.nature.com/articles/s41568-018-0015-6 https://www.nature.com/articles/s41568-018-0015-6