Whether the Nanny is your mother, a neighbour, or hired through an agency, you must be highly alert to the 'toxic' Nanny who turns your children against you, in whole or in part. It is too late when it becomes you or the nanny. This situation is far more common than you might think. There are cases of a Mother-in-Law turning the child(ren) against the parents so that they not only prefer her but believe their parents don't love them. There are cases in which those nice people next door virtually own and operate your children. And of course, there is the Nanny who uses your children for her own benefit. This benefit could be stealing money and items from your home, reporting 'secrets' and sometimes telling them lies which become part of their character.
When you are very busy and believe that your children are being well looked after so that you have nothing to worry about, it may be time to worry. They may be so well looked after that they don't need or want you. Very young children can be so impressionable that a lie told to them by their Nanny becomes the basis of their world view.
So powerful are these lies that even when they become adults the children will believe the impressions they gained, even if the event is proven never to have happened. Adults have repeated "My Grandmother was a Great Mother to me, I love her more than my own parents," yet, when their childhood is explored they will mention many lacks; "I never had a birthday party", "She never came up to school," "She never took me anywhere," yet the first statement (in bold) will be repeated. This kind of 'programming' is not uncommon.
Many Nannies play the sympathy card, and because she has gotten the children to love her so much they will prefer not to go to Disney World if she can not come.
To protect your children from this kind of 'input' takes a lot of effort. Considering you are so busy that you have had to retain someone to help you look after the children it seems a Catch-22 situation.
You can allievate, perhaps even avoid the danger by various methods. The easiest is to have a number of different people and institutions look after your children.
Enrolling your children in a play school, in music lessons, sporting activities, as young as possible, dilutes the input of the Nanny. She may arrive at 7 but takes them to school from 8 to 4. She then can pick them up and take them to another activity, collect them (or you collect them) at six. In this way, the effect of the Nanny is limited.
Taking special days to be with your children is mandatory. You must block weekends as often as you can in which you stay with the children and take them places so that you are there. That you are part of their memories.
Do things as a 'family' even if it is one evening a week when you go to the movies or for pizza, without the Nanny.
Ideally, you should have more than one Nanny; this could be replacing one every six months so that the child doesn't become too attached, having morning or evening Nannies; (your mother can have them in the morning, your sister in law in the afternoon).
Insure that the only truly stable people in your children's life are their parents.