After adoption

For instance, among Indians who participate in the Daily Kos group Native American Netroots, at least four of us have relatives who were yanked away from their families and sent to boarding schools (aji: great-grandmother; me, grandmother and great-aunt; navajo: mother; cacamp: grandparents, parents and himself).

Aji tells the story of her great-grandmother:

[My mom's grandmother] died without ever knowing who or what she was; it's taken a lot of work, years later, to piece her "self" together. Initially, the family thought she was of Scots descent, not realizing that the Scottish surname was that of her by-then-widowed mother's second husband.  Her adoptive name was English. There is no record of what her traditional name (or any surname) might have been; they were more interested in covering up the very fact of adoption than anything else. In the 1870s, the Catholic Church in Michigan was very invested in saving Indian children from an alleged "epidemic" of illness.  What they were really doing was stealing kids and farming them out as fast as they could to reliably Catholic families who would … "save the [wo]man by killing the Indian." No one knows how many were lost to white families via church theft. Hundreds, at a minimum. Probably thousands over the course of one generation alone. But one day in the late 1870s, a good white Catholic couple of English extraction left their home and traveled to the rez for two months, and came back bearing their new little Indian "papoose," promptly given a white name and identity, with never a reference to be made to the adoption, much less from where.
Ironically, when she married, her husband ran his father's logging business, and during the summer months, he traveled around the state; in his absence, she ran the business for him. She hired and fired — you guessed it — Indian laborers, some of whom were undoubtedly relatives, but neither side ever knew it. She died thinking that 1) she was English, and 2) she was the lineal descendant of those English "parents." To this day, I'm not sure how they explained the differences in coloring — probably via the "Gasp! That's not discussed in polite company" method.
Also ironically, after her adoption, her new parents went on to have nine biological children of their own. You'd've thought they could've been a little less greedy about acquiring someone else's child as a possession.

http://www.dailykos.com/story/2011/10/26/1030339/-South-Dakota-kidnaps-Indian-children-and-sticks-them-in-white-foster-care