Yes, I was wondering if the baby had died. I hadn't even thought that "1 year 5 months" was a strange birthday, but yes, it obviously is.
Now, I'm thinking that "Baby" is another pet name of one of these two children on their birthday.
I'm also now thinking that "1 year 5 months" is the time that they've not seen their Daddy, and in fact, that's why they've sent him the card because he's not at home.
Trystan