I would arrange a meeting with the boy's parents and their son. At this meeting I would begin by calmly looking at the boy and telling him how much you want to continue to teach him. Find some positive thing(s) to say about him. Then address the parents and go over some of the instances where their son has hit and kicked his classmates, saying that you want to help them and him in any way you can to control his outbursts and continue to have him in the class. Say something like, "Let's see if we can find out what bothers your son so much that he hits and kicks other kids. Maybe if we know what bothers him we can teach him to come to you or me and tell us IN WORDS what is bothering him. I'm sure we can all work together to make his music class more enjoyable for him and his classmates. Will you help me?"
Then I would turn to the boy and say, "I'm looking forward to a much happier time in class with you. If something or someone is bothering you please tell me right away with your words and we will work something out, OK?" If you receive denial and/or no cooperation from the parents and the boy's behavior continues to regularly disrupt your class, you need to ask the parents to withdraw him.