Absolutely. Start teaching Spanish and Mandarin at age 4 or 5, as early as possible. Kids that young will remember it all and will thank you in 10 years time. I know my kids will be speaking 4 languages before going to high school.
Word. You stole my lines exactly. English, Spanish (in this hemisphere), and to that list add Arabic and Mandarin and they'll be able to speak to any one in the world except the Quebecois in Canada and most Frenchmen, who, for whatever reason prefer no to learn other languages. (I still remember hiking the Inca Trail with 15 other hikers from Canada, USA, Germany, Denmark, France, and England. We could all speak English, Spanish, or both, except the French couple. It was very awkward for them.) Thus in addition to four, they should at least learn the phrase "oł est la toilette?" In case an emergency arises on a visit to Montreal. (I can assure you that the phrase is useful.)
As a start, generally, at least in our nation's two most populous states I'd say Spanish. For New York, it's a tougher call, either Spanish or Mandarin. For the folks way down South, I'd say English. Start 'em as early as possible I say.
