I grew up in a place where I was exposed to a [central] official language (Hindi), a regional language (Kannada) and an [regional] official language (English, in case of Karnataka). So, it made sense to learn a second language in school. English was useful since it was the main official language, and Kannada was useful since it was the spoken language as well as official in some places.
Now that I am in an English speaking country, I started wondering why our children should learn a second language. There is no specific business need to learn another language, as long as you are in the US.
The only reason I could think of was that it would help broaden one's mind. Learning another language allows you to read literature in that language which in turn exposes you to a different culture and thought processes. You get to have a deeper understanding of your own as well as other cultures. I recently read that research has shown that studying another language actually improves your math and verbal abilities. Maybe, this is attributed to the additional neurons and connections made..
Of course, knowing another foreign language will expand your growth and job opportunities. With today's global economy, it makes a lot of sense to be multi-lingual.
Second language is just relative. What is a first language? Is it your mother tongue? Is it your dominant language? I used to think that my first language, as a kid, was Kannada. But, ever since I started schooling in English, and once I started thinking (and dreaming) in English, my first language became English. The dominant language shifted from Kannada to English. So, Kannada is my second language now.
So, which second language should one learn?
According to this site, the most practical second language is French. Hmm, makes a good case.
What do you think would be a good second language for kids growing up in the US to learn?