I read a quote by some wise old Asian person recently... can't remember who... but it went something like: :"Calm parents invariably raise calm children". Something like that. Well it's really stuck in my mind.
My kids fight too. I have noticed though that it's generally worse when my
Dh or I am uptight about something and when we raise our voices over trivial things. I think as parents we set the tone of the house and our kids mirror us.
When i had my thyroid condition really bad last year I was a screaming banshee mum most days... and this is when my boys really started to get into the habit of fighting. Now that I am improving on medication I can almost reflect on things... cause and effect IYKWIM? So I have been recently testing out this old guys saying about being a calm parent... i think there might be something to it. So recently when my two boys have fought I have simply stepped in without saying anything and gently but firmly guided one boy to one room and the other to another room. The laundry is a good place. And then calmly gone to each child. I speak to each separately so that there isn't any injured pride. In a low voice i remind them of what I expect and the consequences of their choice to fight. I remind my 5yo that he won't be getting a treat he was hoping for on the weekend and I remind my 3yo that there will be no dessert for fighting boys... and that if he fights he won't get to help stir the jelly (or whatever, make it more immediate for littlies).
The biggest challenge (I think) is to first stay calm yourself. Divide and conquer. Remind of consequences. Follow through on any threats. Don't make a threat you won't persue. Catch them playing well!!! if in a few hours you hear them co-operating go up to each one and give them a hug saying how much you love it when they work things out together.
Goodluck... count to 10 before yelling. You are the mirror!