The most important thing you can do for young people is get them to sing. Learning to sing songs at a young age develops critical musical skills in children that they can use their whole life. Sing lots of songs.
I generally will start kids around 7 years old, but some can be started a little early. Holding and focusing on an instrument takes some physical skill as well as a developed attention level. I teach kids how to sing and accompany themselves. I do include a method of note reading, but I find the key is in developing rhythm skills and repertoire.
Giving the gift of music to a child is something that can change their lives forever. I have numerous adult students who played an instrument in school, or when they were very young. They all have a story about enjoying music as a youngster and seeking out that enjoyment as an adult.
Oh, and don't forget to support music in the schools!