My kids go after each other right now, similarly, and I don't really understand it either. I think it's developmental and asynchronous and environmental.

My DD is very upset bc I spend "all my time worrying" about DS. She has a point--except that I spend about twice as much time interacting with her. She is chatty, explosive and emotional and DS tends to withdraw.

I agree that having individual time with each child is really important, and that they know how valued and loved they are--but with some kids (like my DD) the bucket is never full.