DD is 4.5 and going through a hitting phase (again). There are two things that trigger it. Firstly, any thing she has to share with her sister, or that her sister takes from her. Lashes out. Secondly, quite often when DP or I reprimand her or tell her she can't do something. It's often accompanied by making faces, aggressive growling or name calling. We tend to put her in time out for hitting, and to take away tv/bike/treats for the other things. But it doesn't seem to have any impact, even when warned. She just does it again the next time. She doesn't seem to care that we disapprove, or get that people don't like children who hit.
I'm not sure what's at the root of all this aggression, or how to deal with it. She clearly cannot regulate her emotions. She knows hitting is wrong, but conflict makes her fearful, makes her lash out. But she has to learn to stop it. She is also defiant and often refuses to do as she is told, but that doesnt worry me quite so much. Until last week when she had a nasty cold, we had about three weeks of pretty good behaviour.
DD2 is 19 months and DD1 is due to start school after the summer. I am not enjoying her company very much at the moment.