It is never, ever too early to start introducing children to music. I don't remember when I didn't hear music growing up. My mom had an extensive record collection and played it for us, so I grew up on 50s standards and big band music. I could sing "Chattanooga Choo-Choo" when I was five.
I think music does for small children what nothing else can do. It engages every part of their brains. I mean, think of how many kids learned The Preamble from singing it with the "Schoolhouse Rock" cartoons on Saturday morning! I was singing it was I was four or five, for sure. I also learned grammar, math and history because of that series.
Music should be an integral part of every child's environment.