Whatever instrument - A kid can play all of them. I mean, you dont really know when it will be useful. Musical instrument teaching accelerates brain development in early childhood, especially in areas responsible for sound processing, language development, speech perception and reading.
Neuroscientists found out, that: when children listen to music, it will speed up language development, reading and other skills. The attentionspan, organization of thoughts and regulation of behaviour is positively affected. These skills are very important in both: school and adult life.
Also children learning an instrument understand early that working hard on something will gradually improve that skill. This is a very important piece of knowledge for children, which can significantly affect their further and especially adult life.