When and how should you teach a small child a foreign language?

I was reading sweetteaindahouse’s question about learning foreign languages in school and someone mentioned that we should start learning them in kindergarten. I like the idea of teaching my (wayyy in the future) children a language while they are young but what is the right age to start? Also, how should you teach them? I would think you would have to learn it or be in the process of learning it too, right? How would teaching them to read and write work at such a young age when they are still learning English and other kindergarten-y things?