what is the easiest way to teach my 6y.o. another language?

The best method is immersion ... at that age children are incredibly capable of learning a new language very quickly. If you speak the language you want to teach your child then just start speaking to them in it. Start off by building vocabulary ... for instance, if you want to teach your child the word for "chair" in *blank* language find a chair and say the word while demonstrating it. It can be a little brutal at the beginning, but if you persist at it you'd be surprised how quickly your child will pick it up.

If you don't speak the language you want to teach your child then I would suggest language courses. It would be preferable to find someone who could teach your child in person ... CD's and DVD are good, but in person interaction is better. If you can't find a place that can teach your child then all you have to do is go to your closest Barnes & Noble or Borders bookstore and find some language books. You can also find online store who sell language material (specifically for children).

You might also want to look in to buying media in your language of choice ... Movies, TV programs, even news in the language you can have you child watch on TV would help in comprehension and pronunciation. The more you can immerse your child in the language the better ...

Personally, I grew up in the Los Angeles area of California in the late 70's and early 80's in a mixed language family --my mother was a French Professor from Denmark. So, growing up we learned English, French, and Danish. And when, I was 12 we moved to Brazil for four years, so I had to learn Portuguese.

Edit: Learning a language on your own (via CD's and Books) is sometimes unavoidable, but it should be avoided at all costs if possible. Don't get me wrong ... language programs like Berlitz and Rosetta Stone are very comprehensive, but I can tell you from personal experience that it is very easy to learn a language incorrectly if you don't have someone there who knows it to correct you. And, if you spend months (or even years) learning a language the wrong way it is VERY HARD to correct the behavior. This can go for grammar and/or pronunciation ... if you learn it the wrong way in the beginning it will hurt you in the long run -- it is much easier to just learn it the right way the first time, and for that an instructor is invaluable (a CD or DVD just simply can't perform the same function ... no matter how advanced it is).

And just an FYI ... I am aware Rosetta Stone has a pronunciation correction function, but I'm going to tell you right now it isn't infallible. It certainly is a good function, but it doesn't work as well as you might think it does. Its one thing to talk to a computer ... its a completely different matter entirely to speak with a native in another language. I've known people whom have used Rosetta Stone to learn Portuguese, Spanish, Danish, and French -- most of them actually learned a lot, but every single one of them had some glaring pronunciation or grammar mistake they habitually committed. This might not seem like a big deal to most people, but in other languages sometimes changing the grammar structure of a sentence can completely change the meaning on what you're saying, or ... quite simply ... could make what your trying to say unintelligible.

Start as early as possible!

Buy movies and songs in that language to listen to whenever you can. Try to practice it at least once a day for at least 30 minutes.

Get a good teacher that can correct pronunciation and grammar.

Put them in a class because peers and children learning together greatly speeds up the learning.

Make an effort to learn it yourself. If the child sees that you value it, he or she will value it more.

Buy your own workbooks and practice books to go over with your child when you don't have any homework from your child's second language tutor or school.

The most important thing about learning another language is to not push and scold, but to make it fun and interesting. Make it something they want to do, and let them do it as much as you possibly can!

I speak three languages, if you do not speak another language yourself, the best advice I can give you is to learn it with them, and speak/practice it at home.

Read books, listen to tapes, and watch DVDs in the language together.

Key to success, show them how to learn it...

A good program for those who a starting out; Rosetta Stone.

Rosetta Stone is the best software for language teaching. Your child can used too its for beginners.