W.C.
Just a few thoughts:
First of all this is a phase, but it needs to be stopped now, or it will get now or it will get worse.
One thing you can do is:
He is small enough that when he starts to act out, hold him close, controlling both his arms and legs so that he can not move or hit you, and say, you may not hit me or kick me. Say it once How him close until he calms down. Then say while you are looking him in the eye, you many not hit or kick me. It is important to stay calm and that is very hard to do.
Another thing you may want to do is to continue to put him in his room with a lock on the outside. That way you have control of when he can come back into the family. Again it is important to verbalize that you many not hit or kick. Do not leave him in the room for more than a minute at his age.
At his age I would do the former, rather than the later.