Granted, I did not have to do this with siblings that were my own children, but, in a variety of situations including those where I have charges that are siblings and in the classroom, I have the attitude that "fair" is not a reasonable thing to expect. The world is not essentially a "fair place." Some people have more freedom than others, some people have to deal with more illness than others etc.
The way this applies to children is that everyone is capable of certain things when they are capable. Of course with new freedoms come new responsibilities as well. When child X can't steer her bike reliably, she can't drive it to the park even though child Y can because she CAN steer as well as follow a number of other safety rules. Before she proved she could handle the responsibliities she wasn't allowed to drive her bike to the park either. When child Y gains the ability to use some new skill, she also has the responsibility to apply that skill in helping with family chores too.
I'm sure you get the idea, but in essence, what is "fair" is that everyone gets the best opportunity mommy and daddy (or I as caretaker/teacher) can give under the circumstances and considering the abilities AND associated responsibilities of the child in question.
YES, this will result in whining, but when they learn that the "its not fair" argument does not elicit either a bunch of attention from you OR a negotiation period, it will stop being the "go to" complaint. I will listen if a person offers up an alternative solution that is a win-win, but only if it is not done disrespectfully, on the basis of "fair" or with a whiny voice.