Interesting article. My middle child is very musical. And this became more apparent each time she added a new instrument. She also became more willing to practice all instruments the more of them she had and did better quality practice for each new instrument added... I was so against her taking up a second instrument because she was lackluster about the first. Adding the second was a huge improvement. I argued that a third was ridiculous, but the school compulsory program was compulsory and so she took up a third and her first two benefited...
In the case of music and sport (and possibly other areas as well), talented children experimenting with multiple instruments or sports will be exposed to more variety of teachers and coaches who will impart instruction which benefits more than just the area of their own specialization. Piano, string and brass teachers will not be providing direct instruction on the other instrument classes, nor will tennis, basketball and rowing coaches directly instruct on other sports, but they will impart skills, habits, body awareness, etc which are cumulatively useful to the child's development across the domain.
