EdG. says
Ship the brat off to a foreign country, let the real world be their classroom.

ultimatelanguage says
You can start by giving them vocabulary cards. The cards contain basic and common languages with their translation. There are also foreign language textbooks and cds/dvds. Just play the cds everyday and little by little they become familiar with the words and eventually they can speak a sentence.
sample of dvd:
http://www.ultimatelanguagestore.com/inc/sdetail/3
or check this site for more language learning materials and related articles.
http://www.ultimatelanguagestore.com/home
Good luck!
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