Why are dad and son speaking english, yet dad speaks spanish at work?

He doesn't solely speak English with the son. He switches back and forth between the two languages, which most bilingual people tend to do among family. I thought it was a nice touch how they used the two tongues. The son could clearly understand Spanish, but never really spoke it, so speaking primarily in English with him makes sense.

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http://tinyurl.com/m746w8t

Very common with second generation immigrants. Even if their parents talk to them in their mother language, they usually reply in English. Reason why the mother tongue is usually lost by the third generation immigrants (as nobody talk to them in that language anymore.)

I am the only one if my Mexican family born in the good old USA and my parents and I spoke both English and Spanish all the time, just like in movie