From a study by Shore, Rebecca and Strasser, Janis:
Hearing causes brain cells (neurons) to connect and neural networks to form. Advanced brain-scan technology and neuroscience research reveal that when children participate in music, the brain “light[s] up like a Christmas tree” in many different areas (Parr, Radford, & Snyder 1998, cited in Isenberg & Jalongo 2001, 159). The growing neural networks eventually become the foundations upon which all other learning is based.
This abstract puts in almost the simplest possible language, the importance of encouraging young children to make music.
It also explains why children who are actively involved in learning to play an instrument tend to do well not only in school, but socially and financially as well. So as we approach the time when the academic year kicks in, and children are choosing activities, it is a good time for parents to encourage children to explore music!