Start em' young

I am a firm believer in starting children up on music as young as possible I say this from experience. I started playing guitar when I was 14 years old, and have been playing ever since. It is by far the most rewarding thing to be able to play music when ever you want or need to. The reason I speak of this is because children are like a sponge, as they grow the ability to just take in the info without bad habits forming becomes harder and harder. So if you were to start introducing musical instruments in your child's life they will eternally thank you believe me. The key is to give them the choice of what instrument they would like to play. The best part of playing music is that it is a window to your soul and sometimes a way to heal it.