Daisy, I really think you are right. I was raised in the 50's and thinking back, I think we were a much healthier and robust lot in general than kids are today. It seems like the cleaner and more sanitized we become, the more kids come down with. I certainly don't remember kids having all the weird allergies that they come down with now - it just didn't happen, not like now anyway.
My boss (who is the same age I am) and I were having a good giggle over this the other day ... how our whole generation managed to survive to adulthood - and without hand sanitizer! Our houses were as clean as our moms could get them with a mop and a broom, but certainly not "sanitized". We rode bikes and climbed trees all day, we played in the dirt and dug up worms, sometimes while eating a candy bar. And we SHARED those candy bars and drank out of the same soda bottles and nobody got sick and died! We pulled the hose out of the mud and drank out of it and we ate tomatoes right off the vine and nobody got sick. We ate candy bars and cupcakes and Twinkies and drank Cokes till they came out of our ears and we survived to tell the tale. And you didn't see nearly as many overweight kids then as you do now either. We ran it off! We were a lot more physically active, a lot less fussed over and petted, a lot more independent, and in general a lot healthier! And we weren't taken to the doctor every time we sneezed and put on antibiotics - if you were sick, if you didn't seem to be getting over it on your own and were getting worse, then you went to the doctor!
I really think that has a lot to do with it. If you're kept in a sanitized atmosphere, never exposed to any kind of germs, never build up the immunities and antibodies that you should, then you're a sittin' duck for the first nasty bacteria or virus that comes along!