Body Movement

I always wonder..... Those violinists who are famous for their body movments during performance (aside from their extraordinary talent), when did they start doing that? When I watched clips of young Midori, or Sarah Chang, their movements are minimal. When I saw Joshua Bell on TV for the first time, I thought he was going to fall backward.
When my son participated in a music festival one year, there was a very talented violinist. She was about 10 years old, but boy, she moved a lot. I really don't remember how her playing was in spite all the advanced pieces she played. His teacher mentioned something like this. Little kids don't naturally move around like that. Only thing he could think of was that it was encouraged or taught. But a lot of grown-up violinists move a lot. Do they help in any way? As a concert goer, it is interesting to see them or their facial expression, but some people are annoyed by it.
When my son was about 8 years old, his first teacher told him to feel the music with body and swing his body side to side like Joshua Bell (She was a big fan of Joshua Bell). Usually, my son is very cooperative, but this time, he refused and stood still. After the lesson, I asked him "Why didn't you swing your body?" He told me "I don't like to move like that! I want to play like Heifetz!" This, I was very surprised. This little boy actually had an idea of how he wanted to play. This was OK by me and I'm glad I didn't force him to move around. Maybe when he is older he may get some habitual movement. Only time will tell....