Does this make me a bad parent?

Today, when Micah came home from school, Zoe picked a fight with him.

I let Micah kick her.

I'll clarify.

I still feel kinda bad, though.

Micah came home and didn't have any homework because this week is state testing. He's really been doing well, and I have no problems with his attitude coming from his teachers this week. He was happy when he walked in the door.

Zoe decided that she was going to follow Micah to his room. I don't usually intervene, because sometimes he lets the girls in, sometimes he doesn't. I leave that to him. It's his choice. When he doesn't want them in, he is allowed to tell them "get out of my room."

Zoe was in a particularly irritating mood (so was Ali) all day, and the girls have been mad at each other off and on all day. This made me watchful when Zoe went to play with her brother. I'm listening from the living room down the hall, and I hear, "NO, get out!" I got up. I went to the door and told Zoe to leave Micah's room. At this point, I know Micah is irritated, and I know Zoe is pestering him, and that really isn't a good combination. It's a brother-sister thing, ya know?

The next move was totally preventable. I could have stopped the whole thing before it happened. Zoe took a crayon from Micah, and I knew that that had to have been what irritated him before. Zoe wasn't listening to me or Micah, so there were going to be consequences. I decided at that point to allow Micah to defend his space. Micah took back the crayon and kicked his sister.

First, before you defenders of Zoe are outraged that I would allow my kid to harm another, I want to tell you that Micah doesn't hurt anyone when he strikes the first time. There are warning shots. Always. It's just how Micah operates. He has a routine, and this is definitely part of it. He is a peaceful kid. He doesn't want to hurt anyone. I know that. It's going through my mind that he isn't really going to hurt his sister at first. Especially since he isn't really in a bad mood to start with.

So I let him kick her. Just once. I then intervened and took Zoe out of Micah's room and took her to her time out on her bed. I explained all about how she is not allowed to just take things from Micah without asking, and that if she wants to go into Micah's room, she needs to ask. She continues her time-out after I have (without her really knowing) check out her leg where he kicked her for bruises or marks of any kind. None. Just as I thought. Warning shot.

Zoe's fine, Micah is calm once she is out of his room, and all is quiet in the house again. So...should I have intervened earlier? Should I let him fire off more than the warning shot? I'm still questioning myself. I just hope Zoe learned her lesson.