This comes from Family Law Prof Blog's Family Law Prof on Custody of Michael Jackson's Children:
University of Dayton Family Law Prof Pamela Laufer-Ukeles contends the nanny of Michael Jackson's children ought to have a legal claim for visitation or custodial rights to the pop star's children, but Grace Rwaramba's status as a paid caregiver will likely squash any chance of that. Her article, "Money, Caregiving and Kinship: Should Paid Caretakers Be Allowed to Obtain De Facto Parental Status?" published in the spring edition of the Missouri Law Review and available at SSRN, explains that state laws and the American Law Institute principles almost always exclude caretakers who receive compensation — foster parents, paid childcare providers and surrogate mothers — from the categories of psychological parents or de facto parents to whom courts may grant such rights. Her article contends that paid childcare providers should not automatically be disqualified from obtaining custodial rights in certain cases.
Indiana has recognized step-parent visitation but to have a nanny with the intensity of a relationship as a step-parent seems to me a rare case. As for third party custody case, take a look at my archive on third party custody.
I do want to commend the original article for reminding people that mother and father are not the only candidates for custodial parent.