I have a very close friend that has a live-in nanny for their 5 kids. They take their nanny and her dd everywhere w/ them. Including WDW, Colorado for ski trips, and last spring to the Cayman Islands. It's not to ditch the kids w/ the nanny. Their nanny and her dd (a teen) are their family now too. So, they naturally include them. I think it's also natural to help take care of them, it becomes instinct when you do it day in and day out.
I'm just wondering how the OP knew for sure they were nannies? In 2003 we took an extended family trip w/ my sister and her family. Everyday in the parks we switched kids after lunch, for the remainder of the day or until the fireworks. Half the reason we took the trip together was to be able to do this. She was actually the lucky one-- my son was 11 at the time so he rode the rides w/ her and BIL. I took their 18 month old dd who didn't really like many of the rides or characters. It was just easier than constantly using baby swap.
I'm just wondering how the OP knew for sure they were nannies? In 2003 we took an extended family trip w/ my sister and her family. Everyday in the parks we switched kids after lunch, for the remainder of the day or until the fireworks. Half the reason we took the trip together was to be able to do this. She was actually the lucky one-- my son was 11 at the time so he rode the rides w/ her and BIL. I took their 18 month old dd who didn't really like many of the rides or characters. It was just easier than constantly using baby swap.