I have two girls 8 and 5. They are the best of friends. When my youngest was first born, we made sure my oldest visited her in the hospital first and bond as a new family of 4 before we had other relatives visit. It is also important to make sure that the kids feel special in their own right and just not labeled as so and so's oldest sister or so and so's younger sister. We take time to spend with one of the girls as well as them together. The most important thing is to make sure that they are loved, they are special and they are very blessed to have one another.