So what is up with Sibling Rivalry? Who is worse? boys or girls?

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I had my granddaughters over today and if it wasn't for the rivalry they would be perfect.When my sis and I were little we had knock down drag out fights. I had only one son so I did not have that to contend with. I wanted boy grandchildren. But now I have the girls and I have never loved anybody more except my own son. They are so different. The little one is two and the oldest is four. The four year old is sometimes so mean and the little one is a "monkey see,monkey do." SO if the oldest gets in trouble the little one follows. But I have always gotten them different colors of toys and they choose but then they always want what the other has. What do you think:boys or girls? Who is the worst?