My brave little boy,
I know that I told you I would do my best to be home for the party, but I am afraid that I have to stay here a little longer still and do my part in the war. I know you must be disappointed at this news and I am very disappointed too!
Here's what we will do. When I come back we will have another birthday for you, with a cake and songs and games. So you will have two parties instead of one.
What a lucky little boy you will be! I am counting the days until I can see you and your sister again. Mama says you have grown very big, and I am proud of you for being the man of the house.
Enjoy your birthday, and remember we will have another party when I come home!