Learning a foreign language at very early age is always a good idea. Why? Because we get too much exposure much easier (e.i. for English, there are a lot of cartoons, books for children, songs, PC games, ... ) and also because the kids will not get nervous when they make a mistake. Totally opposite, they'll smile and they will correct their mistakes slowly, step by step.
Plus, kids are the active almost non-stop and they are so positive. That's why teaching them sometimes can be challenging but generally it's very good.
The conclusion: The kids are the ones who learn foreign languages much faster but they also forget easily. Therefore, repetition is essential for them.