I think that goes for most healthy people, including adults. I know somebody that is constantly using hand sanitizer and sanitizing wipes to clean everything in her office *esecially* when somebody in the office is sick. Guess what, she is the one that is always getting colds and flus. No exposure = no immunity.
Yes, this is true -- although I never use hand sanitizer and I often get colds. Though that seems to have been happening a lot less since I started vaping.
My point though was that childhood is a critical time for development of all things, especially an immune system, which is why I say that children should be allowed to reach a certain age before immunization should be given -- and then just for the known bad stuff that can kill or seriously sicken them if contracted.