I heard my children argue this morning and it occured to me, they never hit/push/shove each other. I remember as a child older siblings routinely hit me. It was the same at cousins/friends houses, siblings often hit/pushed/slapped each other, it was nothing unusual or commented on. I don't think kids do this so much anymore (?) Good! They did hit as toddlers but probably grew out of it by three years old.