1 - Be supportive - Someone once asked Mickey Hart of the Grateful Dead how to become a professional musician. He said, "First rule - get good parents!"
2 - Encourage experimentation - Banging on pots and pans, scraping a violin, or screeching into a clarinet can be pretty grating on adult nerves, but that's how the good stuff gets started.
3 - Never forget, on a musical instrument there is no "wrong" - Miles Davis said that...you gonna argue with him?
4 - Encourage diversification - Let 'em try lots of different instruments. After all, did you know you were going to be a neurosurgeon at the age of seven?
5 - Don't stage-parent - There's a big fat line between supportive and pushy. Of course your child's talented...but not at EVERYTHING!!!
6 - Encourage diversification, Pt. II - Once Junior decides he likes his instrument, he'll get better at it by being a well-rounded person. Sports and other recreation are important, too.
7 - Discourage diversification - Diversity is important, but not when parents insist on involvement in Scouting, Church Groups, Organized Sports, etc., which leave a child with no time to be a kid.
8 - Parent actively - Don't complain about your kid being overweight, spending all his/her time on video games, or getting into trouble if you're not available as a good role model.
9 - Don't be a hypocrite - Almost the same as Number Eight, but with a finer point. Being a musician is all about being able to fit in. A child can't do that if he doesn't learn to trust in people.
10 - Be supportive - Yep! We're right back where we started. Obviously, this is the most important rule.