My DSs are 6 and 9. They're great mates, share interests, play well together, clearly really love each other.
But there are inevitable disagreements, arguments over whose turn it is on something, whether it was a goal or not, who should choose the TV channel and so on. More often than not, when they are disagreeing about something, they will hit or kick eachother. It's usually just a couple of hits, then they stop, often when I walk in and catch them.
I had a brother (he died age 20) and we never ever argued, we really didn't. Obviously I know that was unusual, but it means I'm not sure what the "norm" is.
Are my two just normal siblings, or should I worry about the level of violence in their little spats? I this a boy thing, or are girls this aggressive?