This is one thing that my mom allowed which I swore I'll never do when I have kids of my own. My son doesn't have a yaya (nanny) but if he has one, I will never let the yaya give any form of discipline to my son.
It's the parents responsibility to teach good manners and to discipline their kids. God gave them those kids, not to other parents, not to the yaya, so why give the big responsibility of disciplining their children to the hired help. Their upbringing is different from the parents, so their own views and ways with regards to discipline is probably different from the parents as well.
At the young age of 10, I questioned my mom's decision. I didn't talk to her about it though. I just didn't bother getting close to the yaya. That was probably my way of showing everyone that I don't agree with my mom giving the yaya free rein to discipline me and my sisters.
My sister C though was very close to her. I remember one time, we were having lunch, and my sister and the yaya were whispering and snickering while giving me sideway glances. "Don't you know that it's rude to do that in front of other people?", I angrily told them. I don't even remember anymore but I think my mom asked me to say sorry and leave the table.
I guess my mom was just so busy with work, she needed other people's help to teach us what is right or wrong. There were times when she also ask her sister to buy for her the things that we, her 5 daughters, need, like materials for my sisters project at one time. I understand that she needs to work but she could have just asked the yaya to inform her when we do something naughty and discipline us herself.
What about you, will you or do you allow your helpers to discipline your kids?