I disagree with what was said above, that you can only have one native language. I know about many who have grown up bilingual, and the languages don't even have to be related to eachother, for you to know them both as mother tongues: In my country there are whole municipalities where people have two mother tongues - Norwegian and Saami - and those are not at all related.

My native language is Norwegian (though I also consider Saami to be "my language", even if I can't really speak it).