N.
There was a girl I went to high school with who did the exact same thing you're describing. She was perfectly normal in every other respect. She was bright, in regular and honors classes, and actually a very beautiful popular girl, she just had this twitch. I always thought it was maybe a form of Tourette Syndrome. I know there's something called a Tourette Tic. I read a little about it on this website http://www.tourettes-disorder.com/symptoms/tics.html. It makes mention of common childhood tics that vanish within a year. With your child being so young, maybe that's all your child has. Do a little research on tics on the Internet and you may find your answer. And if your child's current doctors can't give you an answer, I'd definitely be checking with some different doctors. Good luck!