It seems to make sense that the earlier they're exposed to a second language the sooner they'll learn. The only problem here is that when the second language comes to take place of the native language which has never been allowed to develop properly. Children should be proficient first in one language when introduced to another. This way, they'll be no confusion. I've also read in one magazine that the studies show that the most advisable age for one to learn a new language is during the early adolescence, that is somewhere between eleven to fifteen. Hope this helps.