During the early stages of the French and Indian wars, 1754 to 1756, there was a major effort by the Seneca, Delaware and Shawnee nations to destroy English settlements in upstate New York and central Pennsylvania. The adults and boys were killed, but young women and very small (under the age of three) boys were taken as captives. These were violent acts of war and it would be hard to call them an altruistic adoption. After the captives were taken deep into Indian territory, they would distribute these captives to families that had lost loved ones and who would then slowly begin to integrate them into Indian societies.
The best single historical source about this process is "Indian Captive: The Story of Mary Jemison" which is based on her own diary and edited by Lois Lenski. Other sources include "Calico Captive" which is based on the diary of Miriam Willard and edited by Elizabeth George Speare. or "Captured by the Indians: 15 First Hand Accounts" by Frederick Drimmer. My own favorite book on this topic is "I am Regina" by Sally Keehn. This is historical fiction, but is based on the life of Regina Leininger. Regina Leninger did not leave a diary. She was captured at the age of ten and was not liberated until she was 18. Sally Keehn did extensive research on the life of early German colonists in Pennsylvania and the Shawnee nation. She was also deeply influenced by the diary of Mary Jemison. Her book is also much shorter and easier to read than the more authentically historical books mentioned earlier.