Adoption through kidnapping and raiding was a common practice in many Native American groups in North America, yes. The reasons for them are diverse and cultural, but it is true that Comanches practiced it. One of the most famous examples is Cynthia Anne Parker, who was taken from her family's ranch in Texas at the age of 10 in 1836 and raised as a Comanche woman by the name Naduah. She lived as a Comanche for more than twenty years, married a Comanche man named Peta Nocona, and had several children with him, including Quanah Parker, a Comanche warrior, diplomat, and leader who lived until 1911.

Parker's case is particularly notable because it was infamous at the time and remained a popular story for quite a long time thereafter - her relative's search for her inspired the 1956 John Wayne western The Searchers - but it was just one example of a huge and popular literary genre called "captivity narratives." It is also worth pointing out that though the film ends with John Wayne heroically rescuing his niece, the real story ended with her family locking her into an attic to prevent her from escaping back to her Comanche family.

These stories predate European contact with Native Americans but share a lot of the racial assumptions about the people doing the kidnapping; namely that they were technologically backward, "savage," and living in a "state of nature." Mary Rowlandson, a New England woman captured by members of the native alliance in King Philip's War, wrote one of the most high profile captivity narratives in the late 17th century: The Sovereignty and Goodness of God or, Narrative of the Captivity and Restoration of Mrs. Mary Rowlandson. Many of the elements of her story were repeated in later narratives. This is only in part because the social practices of various Native people were similar, but also because captivity narratives themselves are a socially constructed element of white society facing Indian society: writers include elements that are expected, within a moral framework that is meant for consumption by a white audience. Even the titles of Rowlandson's work neatly summarize the thematic and moral structures which they reinforce: captivity, "goodness" contrasted against "savagery." It's implied here but it was not always so: consider Cotton Mather's account of Hanah Duston's captivity entitled Humiliations follow’d with Deliverances, which even more succinctly reflects the theme.

But the short answer is yes, absolutely, children were sometimes raised among Native groups as members of that group. While these children often straddled cultural lines and lived with one foot in each camp - such as William Wells or Apekonit of the Miami, who also served the US state as an Indian Agent in Fort Dearborn - narratives that surrounded them stressed the cultural barriers between "civilized" society and "savage" society, and put them within a common moralizing framework intended for consumption by white audiences.

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Though it should not be read without some skepticism, SC Gwynne's Empire of the Summer Moon spends a good deal of time with the Cynthia Anne Parker story and gives a extensive biography of her son Quanah, as well.

Adolph Korn was 10 years old when he was kidnapped by Apaches from his Texas home on January 1st, 1870. He was passed on to a band of Comanches and adopted by a family and became a member of their tribe. He was seen seven months by another white adoptee where the two boys plotted their escape, but by the next spring he had become fully assimilated into the Comanche way of life. He was returned to his family three years later and lived a solitary existence among his family. He spent the last days of his life living in a cave, away from other white settlers. Scott Zesch, his great nephew became interested in Adolph Korn's life and began researching his history.

This search expanded as he learned of other children who had been captured and adopted by the Indians. Temple Friend, Minnie Caudle, John Valentine Moxley, Rudolph Fischer, Herman Lehman, John and Clinton Smith and Dot and Banc Belle were also captured and adopted along with Korn. To our benefit he compiled his research into a book and published it for us. "CAPTURED" by Scott Zesch is an excellent read if you are interested in what life was like for these children before, during and after they lived among the Indians. The lives that these children lived are particularly interesting as almost every one of them did not abandon the ways of their adoptive families.

Other books that might interest you are "The Blue Tattoo" by Margot Mifflin which is about Olive Oatman who was captured and adopted by the Comanches and "The White Indian Boy" which is Elijah Wilson's biography of the time he lived with the Shoshone Indians.

One other book I would recommend is Frederick Drimmer's "CAPTURED BY THE INDIANS: 15 Firsthand Accounts, 1750-1870."