We started teaching our boy when he was 2 yrs old, and now he is 14. My husband and I took turns to teach him some Chinese every day. We were challenged by him many times and we always found a way to convince him. Now, he has been enjoying reading many novels in Chinese and we can't teach him much since his level got so high. The key is not to force, but to lead properly. For god sake, this is a language, it has to be fun and interesting.