In my therapy practice the issue of sibling rivalry is a recurrent theme. Francoise Dolto was a very popular French psychoanalyst with her own radio show in the 70's. A lot of what she said is very sound advice even in our time. It is a pity that she has not been translated, or has been barely translated into English.
I will be posting some excerpt of her radioprogram, related to topics that come up in my practice and that have relevance for parents today.
"About the birth of a new sibling. The older child might say: 'But why? I don't want it.' 'But that baby is not for you.' However, in many families, parents announce: 'A little brother or sister for you.' The child then immediately expects to have a friend of his own age, as he knows other children who have brothers and sisters. So he thinks 'that will be immediately.' 'But you know that you were born a very small baby.' You show him photos: 'See what you were like when you were little. That is how the baby will be born.' And if the child decides: 'If it is a boy, I don't want it,' or, 'If it is a girl, I don't want it,' you might answer: 'But, you know, it is absolutely not necessary that you love your little brother or sister. He will have parents just like you have parents.' The child that is told that he does not have to love his sibling, will love him or her the most, as it is very natural. When he says that he does not love hiis sibling, it is only to say something silly, to oppose his parent, to push her buttons."
(Lorsque l'enfant parait, pg 22)