Slightly off topic, but still relevant to language learning. We have an amazing "WAVE" of interest in Ireland for computer programming amongst kids - hacking and geek has suddenly become popular and cool.
Point is, kids are learning to program in html, html5, php etc etc, and producing games and apps adults are in awe of. The founders are an entrepreneur, Bill Liao from Australia, now living in Cork, and a 19 yr old Cork student, who now runs his own company. Bill starts the kids as young as 6 or 7, and the free clubs welcome kids up to about 17. The clubs are called Coderdojo s if you want to google them - now all over the world!
Between 7 and 17 is the time to teach kids new languages (inc programming) as the younger they start, the more likely it becomes a native language, as opposed to being "fluent". I am in awe at what these kids can produce, so it's never to early to start with them.
I do agree, that kids can get confused, for example, my brother is married to a french girl, the kids didn't actually speak until they were 3 or 4, but then both english and french came out - both fluent. They speak english now as first language but french is right there too as their Ma constantly speaks in french (esp when giving out LOL)
It's just so sad that we as adults cannot learn so quick...