Well if you come from Russia at age 6 or something and you forget Russian, and don't speak it from then on(adoption), I would say that Russian is still your native language. Maybe English is a second native language, just my opinion. But I do believe that the language from birth is the native language.

eh not worth speaking of, its already been discussed as it was mentioned above. But for me since my English is currently better than Russian, I would never say English is my native language. Russian is the language I knew first. Just me.