Dear Little Brother,
I am your big sister. I came first. Try to remember that. I thought I'd take a minute to fill you in on how things are going to be from here on out, since you're a rookie.
First of all, enough with the crying.

Baths are good for you, and frankly, you're a little stinky.
You'll find that we're going to get the most excellent toys in the near future. The Star Trek walkie talkies? All mine. I will, however, share the Stretch Armstrong. After all, I can't stretch it by myself.
The smile?

Well, it needs some work. I think it might take a long, long time.
In the coming years, you and I are going to have some great adventures.
When you are six and I am nine, we are going to spend an afternoon together in our new house, without any furniture, sitting in front of a picture window, waiting for our parents and the movers to arrive. There is going to be a big storm, almost something akin to The Wizard of Oz storm. We will be petrified, but emerge victorious and unscathed, just like Dorothy and Toto (yes, clearly you're the dog in this scenario, the shoes are MINE). When we're sure all is safe, we will grab our umbrellas, go outside under the still dripping trees, and sing Singin' In The Rain while dancing along the winding brick walkway.
We will both be Harriet the Spy, using an old make-up case as our spy kit, containing a notebook filled with observations of our Whackadoodle neighbors, and sneak around the yard and hide in the our dog house clubhouse.
We will build a teepee in the backyard, making it out of wood and a clear plastic tarp and furnish it with lawn chairs and a yellow plastic table. We won't know what to do with it after it's built, but it'll be pretty darn cool.
We will fight and argue and swear never to speak to one another again. And then we'll forget that pact we made with ourselves and start talking to the other without even thinking.
When I graduate from highschool, you will give me a card and sign it "Riot," what you say will be your future stage name. After that card, for some reason, that name will never come up again.
We will grow up, and life will move forward. It will turn out that you're a pretty cool uncle. But let's keep that just between us. I don't want the word getting out that I might actually like you.
Here's some of the stuff I'm going to keep under wraps later, and am telling you only because I know you're not going to understand right now.
You are going to grow up to be one of the smartest people I know and a brilliant musician. You will make me belly laugh like few in this world will. And my kids, which are just the tiniest of a glimmer in my eye right now, will think you're the best uncle ever.

I think I've gushed enough for now, and you're back at the crying so it's time for me to finish up.
Just remember this: although you're going to be almost a foot taller than me, I'm still you're Big Sister, so you've got to do what I say. That's the rule. Mom says so.
Oh, and when you break the window in the storm door one day when you're a teenager, it was ALL your fault. I had nothing to do with it. Tuck that nugget away for future reference.
Happy Birthday Little Brother,
Your BIG Sister