title_body: Is there anyone that has a conlang as their first/only language? It seems that people generally use constructed languages in very limited circumstances, or within small communities that speak the language.  Thus it seems to me unlikely that one of these languages would every be someone's first or only language.
  
  Are there any documented cases of a child learning a conlang as their first language?
upvoted_answer: Yes. According to Wikipedia, Esperanto has 350 native speakers (data 1996). There is also a story about a linguist only speaking to his son in Klingon, but even though the child picked it up somewhat, later in life the child stopped speaking Klingon. Currently, he doesn't.
  
  Also, see Esperanto native speaker AMA on reddit and a blog I enjoyed about speaking Esperanto natively.