My daughter's "mother tongue"

Being an ESL teacher in Italy I obviously teach English to a lot of Italians.  Many of my lessons are individuals since I don't usually work evenings, and many of these are conversation lessons.  One common question my students ask is: "Does your daughter speak English?"  To me that is the silliest question ever!  OF COURSE she speaks English!   But it comes as a shock to most people.  They ask how I manage to do it, and "doesn't she get confused?" and most recently, "what is her first language?".  This one got me thinking.  According to the standards set by Cambride (I am an oral examiner for their exams), English is not considered her mother tongue. But in my opinion it IS.

From the time I got pregnant I decided that I would speak exclusively to her in English, no matter what, and over the past four years I have stuck to this vow.  She therefore had a very clear idea of who spoke what and until recently she has always responded to me in English and is easily able to flip into Italian if necessary without a second of thought.  I say until recently because she now attends preschool at the local school and is learning a lot of new vocabulary at school, that I don't necessarily use, so they occasionally get thrown in here and there.  For example today she said "mommy, you know I sure have a lot of terra in my shoes, I need to dump them out!" 

So why do I think that her first language is English?  For a few reasons.  First, when she began speaking her first words were in English, when she started making sentences her first sentences were in English and last summer at the age of three upon our return to Italy after two months in America, she had completely forgotten how to speak Italian, she could only remember a handful of words.  Another funny thing is that when she talks in her sleep it is in English.  

Another reason that I think it is her first language is that the level of English that she uses is very advanced for her age.  She uses many synonyms and has a very large vocabulary. Whereas in Italian she has the vocabulary of a four year old, which is her age, and of course completely normal but making a comparison between the two she is more advanced in English.  

I don't know how she will continue to develop once she is in Elementary and secondary school, but my hope is that with annual trips to America and continuing to speak to her in English  she will help stay ahead in her English.