Oh gosh David -- what an awful thing to have happen to you!!! I don't think you used excessive force - I think the little brat needs some SERIOUS consequences and a 3-day suspension won't do the trick. He needs anger-management counseling and his parents need parenting classes. It is quite obvious that he is used to getting his way and determined to do so. He also most likely bullies the other kids.
And this was a THIRD grader? I 'd hate to see what he does to his middle school teachers in a few years if SOMEONE does not take strong measures to teach him self-control now. How typical to try to place blame on the teacher.
I hope you're all right. If he was punching you (aside from that kick) I expect you'll be bruised and sore for a couple of days. If you have bruises, for gosh sake go to a doctor and get it documented. You might need that documentation later on if this situation gets out of hand. Let's just hope the admin backs you up and does not kowtow to the parent.
Keep us updated ok?