I ahve a boy and a girl and they ADORE each other. They are pretty much together all of the time. When J is at Kindy, E pines for him!
They are the best of friends.

We are not having any more, so there will be no issue of the odd one out.

I had 2 sisters, and we are still colse.

DH had a brother 12 months older and a sister 18 months younger. He was always very close to his sister and still is. He basically has no relationship with his brother. I suppose my point is that the sex of the child doesn't always determine the adult relationship.