A babies ear starts to listen for the sounds around and be able to think them in their brain. This process is called audiation. A music rich environment will provide a baby with the developing stimulus to think musically. When the brain and development of vocals are ready, a baby begins to imitate the sounds she has heard. In speech, we refer to this as babbling. In music, we can start to hear the sounds of singing. These beginning vocalizations develop overtime to sound more like words/songs and the brain begins to associate meaning with the sounds. Children begin to interact and communicate with these sounds.
This is the beginning of music education. It starts with providing stimulus for the brain, developing the ear, and vocalizing.
For more details on this process, visit the Gordon Institute of Music Learning.