Conceivably have you hitherto endured a cold virus? Perhaps did you get rid of the infection? Certainly you did! You can't cure a cold directly, yet your immune system generally establishes resistance to a certain cold virus within a couple of weeks. We call that healed by your own immune response!
Grownups have actually previously had a lot of the rhinitis infections. Grownups have established resistance to the ones they have actually had. Therefore there are not quite as many runny nose infections remaining for parents to become infected with. That is why parents only get a couple of runny noses per year and youngsters acquire 10-12 runny noses per year.