Wild Child

feral
adjective
1. Existing in a wild or untamed state.
2. Having returned to an untamed state from domestication.
3. Of or suggestive of a wild animal; savage.
"feral." The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. Answers.com 23 Nov. 2005. http://www.answers.com/topic/feral

Fair warning: FeralChildren.com is heartbreaking.