Child management differences

I have been working with children for 8 years and have 5+ years of nanny experience. I currently am working a nanny job where the mother and I clearly do not use even similar management skills with children. Her 4 yr. old son is having trouble understanding rules and boundaries because mom makes up the rules as she goes. When he is with me, he minds, as soon as mom gets home, he runs wild. And she does nothing to stop his unacceptable behavior. She has said to me that nap time is important to her, yet I have watched her keep him up and going through his typical nap times on several occasions. Then, when he acts out, she spanks him. I will never, personally, spank a child, and I have NEVER had to. But, I fear that these things are being solidified in him and I am not comfortable with it. The reason I am here is that she will be out of the country for a year and needs me to care for the children while she is gone- but are we all being set up for failure? The kids will be in for a pretty rude awakening once she's gone if something doesn't change. I understand that she may not see any of this to be a problem, and so we may have to both just cut our losses and go, but I truly love this family, and have actually returned to them after having worked for them years ago. I moved halfway across the country to be here. My question is this- How should this matter be approached? Obviously, it needs to be addressed, but I am not sure how to go about saying some of these things without her thinking I feel she is a bad mother, which she is NOT.

Thanks for your input.

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