A.H.
Jim Fay's Love and Logic books are so helpful with this kind of thing. I have a 3.5 year old son and a 2 year old daughter. I can relate to what you are saying. Sometimes I do feel like my son gets the brunt of some stuff for being the eldest and a boy, but the Love and Logic philosophies really help keep the fairness on an even keel. What I like most is this example of fairness: fairness is not the SAME treatment for all individuals. Fairness is giving what a person needs when they need it most. And it can look different from child to child. Jim Fay is all about sharing control, giving choices and giving empathy when a child goofs up. So I always try to keep this in mind with my kids. From what you wrote I am guessing your youngest daughter acts up at a park or while getting ice cream and you feel your only choice is to go home, which automatically ends your eldest daughter's fun even if she wasn't causing any trouble? This is what I would do in that case: Give your daughter two choices that you are ok with. (Would you like to play on the swings or slide? Would you like to ride the teeter totter or play in the sand? etc. Give her a ton of choices like this so she feels like she has some control over her own decision-making. I think doing that eliminates 95% of a child's misbehavior. If she cannot decide within a short amount of time ( a minute or two) say you will decide for her. After awhile giving so many choices and letting children call their own shots (within your given boundaries) lets them trust that we aren't trying to treat them like a puppet in which we control all the strings. At this point you can say, "I see you are having a tough time making a decision so I will make it for you this time." Or when it is a situation that you must make the decision you can reason with "Doesn't mommy usually give you lots of choices to make decisions on your own? This time I have to make a grown-up decision. I need you to help me out. Thanks."
I have used these books as a teacher and now as a parent. I highly recommend their workshops and liking their facebook page if you are on facebook. They give a lot of great tips there too.
It sounds like your eldest daughter is understanding. I know my daughter went through a phase around 18 months that it was harder to reason with her, so we just stayed home for awhile. Plan some one on one time with your eldest so she can see that you aren't deliberately trying to punish her because of her sister's antics. Good luck and I hope this helps!
A.