I have heard, and I believe, that children can learn languages much faster than adults.  I know my son has some crazy instant recall and remembers very specific things that we talked about or that he saw on a show over a year ago.  But children typically don't have the desire that adults do and learning a language takes desire.  Especially if you're not immersed in the language, i.e. living in a place where it's spoken as the first language. 

So I'd say that if my son & I lived in Mexico he'd learn Spanish much faster than I would.  But living in Canada he wouldn't have the motivation it would be a lot of pushing.  If a child wants to learn a langauge I have no doubt that they could do it very easily.

I agree with Dave. Children really don't see the point in learning another language. I work as a teacher to both adults and children and the adults seem to improve more. It's because they want to learn. They take the homework seriously and try in class. I have to use a lot of my energy with children trying to get them to participate. It's hard to make everything fun and interesting.

From my own experience, my mum put me into French classes when I was young and I just didn't learn much. In total I sat through about 6 years of classes at school as well as the extra classes she paid for. Then when I was 17 I suddenly saw the benefit of speaking another language. I went to Spain to study for 2 months and even before those 2 months had passed my Spanish was already better than my French.

Sure, it's beneficial to start at a young age, but an adult with the right (positive) attitude can do just as well -- life experience is really useful in interpreting communications that might not be entirely clear to you. Any one of any age who believes they're to old -- it will be a self-fulfilling prophecy. The true advantage to starting early is simply that you'll have more time to enjoy your languages.

The kids have a big capacity and learn more easily than a adult I think they should learn after they know talk, my kids will have 2 native languages and the language of the country they will learn in school :)

I think from 0 to 5 it is the most important period of time to become bilingual in future, the same way to learn your mother language.