One of my friends recently welcomed her second child. Wary of how her son would accept the newborn, she came up with a genius plan that I plan on using.
When an older child comes up to the hospital to meet his new sibling for the first time, have the infant waiting in the nursery with all of the other babies. Then when your first born arrives, you and your spouse can walk him down to the bevy of babies and ask him to pick one out. Obviously you guide him to his actual kin, but it is a rather sweet and thoughtful way of including him in the process. Another tip — you might want to mention that the package is non-refundable.