That's the best first word EVER! What is even better is, you are keeping a priceless journal for your children, and their children, and so on....this is a true treasure.

When my children were growing up, various people told me I should keep a book for each one of my four children, and write down the funny or profound things they said, because eventually I would forget. Unfortunately, I could not find the time, and now I wish I had. 

You are creating an amazing treasure for your children here, and I'm so happy for you, and them!