Linguists and language pathologists have long said that children 6 and under can learn a second (and even third) language perfectly.
and internalize it.
Moreover, they never confuse the languages. (If you have that 'snobby' friend who occasionally "slips" and says: "Oh, my -- I just lapsed into German!" chances are they are being pretentious showboats.
The idea of learning a language in high school for most americans is cumbersome—and with good reason. Namely, being about 10 years too late.
If day care, pre-school, and kindergarten schools had a secondary and tertiary language, we'd have a generation of fluid English, Spanish, and (whatever) speaking children.
Learning a foreign language also helps keep your own language grammar intact. Even as a late-starter, altho' I probably will never internalize French or German, they've helped me understand ENGLISH grammar better than ever before.
I know what a relative pronoun is... I know what it means to split my infinitives... Learning other languages gives one a respect for their own. Imagine having generations of children with that respect natural inherent to them, as opposed to found late in life?
Beyond that, there's always been a group of philologists, linguists, and behavioral psychologists who wonder if language shapes the mind. I'm not referring to the 'you can control thought via language'. But the structure of language must play a part in the development of the mind. English is an extremely analytical language. No case endings (except some Old English carry-overs like 'ox' and 'oxen'), a modifier before the modified... having a language structure like that has to affect the brain differently than one that natively deals with a more contextual language with tonnes of case endings, a more fluid -- and open -- word order structure.
now, imagine a child that has, by the age of 6, internalized two or three languages and their weird ways of handling the simplest of statements...?
yes, i think america could benefit greatly from multiple languages, just from the alleviation of our US-centric snobbery alone!
but it'll have to be done way before high school and junior high. the longer you wait, the more of a 'chore' learning languages runs the risk of being for kids.
(wow. that was unnecessarily long just for me to say 'yes'.)