Hi L.!
My daughter turned 3 in August and just got sick for the first time with the flu and has never had a cold. Since she was just over 1 week old and just got out of NICU (preemie) she has been exposed to all kinds of things... from spending over a week in the ICU with her older brother, taking friends and visiting them in the hospital, going to friends homes while kids are sick with fevers, stomach issues and colds etc, and having therapists etc come to our house while being sick. I have NEVER avoided illnesses!
I just asked a Dr last week about how she has gone so long without so much as the sniffles and if her controlled exposures had something to do with it as I have believed for the last 2 years when everyone but her has been ill. He agreed 100% that it def makes a big difference in building a natural immunity to these illnesses. Although he does not encourage this to be done with anyone with a compromised immune system. He says that between the exposures and her vitamin intake that is what has kept her so healthy.
This is the first year that I have given her the flu shot and the H1N1 shot. She got sick 3 days after the H1N1 shot... not that is what caused her to get sick but it compromised her immune system since she had a major allergic reaction to it. Otherwise I think she would have even avoided getting the flu.
The flu she just had is suspected to be the H1N1 one since she got the flu shot over a month prior. It lasted her only 3 days of fever but a week of the rest of the symptoms. The Dr also agrees this is because of exposures and vitamins.
I obviously am not suggesting to go out and have a child lick the ER floor or have people cough and sneeze all over him... but to expose him in a controlled enviroment such as your home to your other child should not cause major issues. Of course using proper hand washing etc too!
I hope you guys all have a happy and healthy winter! Many blessings to you and yours!