Well, my first baby, it's been a decade.
Could it possibly be that you are double digits?  It blows my mind.  You are so tall and so mature and grown up and yet, I remember, very vividly, how you felt in my arms when you were a tiny baby.  Maybe this is the conundrum of motherhood.
Like all your brothers, you were the first to have a silly nickname (and I think your dad might still use it every once in a while if I know him) -- you were always Buster Brown.  In fact, for our wedding (your dad and I's), I looked everywhere for Buster Brown shoes for you to wear (and I found them)...and still have them.  
You were a surprise.  You will always know that, I'm sure.  However, you were a surprise that changed my life and my mind and my personality and just about everything about me.  Your little life (at that time) changed me into a mother.  Although I was a student and an employee, you came first.
This will embarrass you, I'm sure, but I was so committed to breast-feeding you till you were one that I carried my tiny battery-powered breast pump all over campus with ice packs in my backpack so that I could pump between classes when I was away from you for too long.  There are some stories about that -- I will wait and tell your future wife when you have children of your own.  
You, Robbie, are a very special child.  I don't believe it's because of me, or your dad, or anyone.  I think you were born that way -- with the ability to empathize and feel things that other people feel.  Sometimes you will hate this ability but it will ALWAYS and I mean FOREVER serve you well in your relationships with other people, be they your guy friends or your significant others.  You have a sensitive heart and I love that about you.
Sometimes I wish I could take away some of your intuition so you didn't always know how I feel and feel it too.  But, that would mean changing the essence of who you are so I will hold on to the thought that rocks that have strong water run over them become smooth and polished and brilliant.  I have no doubt that you will be a beautiful soul because you already are.
You are my questioning child.  You want to know the 
real
 answer for everything.  I admire that about you.  (And the real secret is, I was the same way and drove my teachers crazy).  
However, you are also the most teachable child I've ever met.  I love watching you with your teachers and coaches.  I feel so proud at the boy you have become.  
You have a fabulous personality, Robbie, and it will get you places.  Make sure they are places you want to be.  You have a lot of influence over your peers.  Use it for good.  (I think that's a Star Wars reference).  
I know that I am hard on you, darling boy.  I'm sorry.  I try to remember that you are only a boy.  I will keep trying.  I expect so much of you because I know how smart and capable and willing you are to learn.  You are going to be an amazing person, Robbie, and you will change your world.
I love you, Robbie.  My firstborn, the child who introduced me to true, unconditional love.  
Happy Birthday.
Love,
Mom