What is your Mother Tongue?

Just the other day I had lunch with a group of Japanese friends and their kids. My daughter was running around screaming laughing and generally having fun with everyone. Her Japanese is great I thought. It seems to be her dominant language these days. Funny how 'mother tongue' is used to refer to our native language. The language from our mother. But right now, my little girl speaks more Japanese than English, which is my mother tongue. Japanese is the language of the country she lives in. So it doesn't go to say that your children will speak their mummy's language when living in another country. Is that why we don't hear the expession mother tongue so much these days? The power of friends and community seems to be stronger than that of mummy when it comes to language learning!! Oh and I must not forget the power of daddy too!!!