The Gag Reflex

I've been changing poopy diapers for over 4 years now and you would think that my nose would have adjusted to the smells. As any mother knows, changing a toddler diaper is a far more traumatic experience than a newborn diaper and Baby Boy's diapers at the moment are no exception. I've had the pleasure of babysitting my friend's kids a couple times this past week and was caught off guard by my diaper changing experience.

My question - why is one's gag reflex so much stronger when changing other children's diapers? Does one's nose actually know the smell of your own children?