Can Siblings Work Out Differences Between Them on Their Own?

Today is a wonderful day. The sun in shining outside and my daughters are enjoying breakfast and arguing about playing with dolls, even now as I write. I consider it, "getting to know my sister time." They can and do work out many of their differences even now as 4 and 9 year-olds--on their own. They are learning about each other through these arguments and establishing the foundation for their adult relationship with each other. Do you break up arguments with your children? Do you encourage/make them apologize when they have caused harm to their sibling?