That's a good idea!
Also, I didn't do any professional photos of DD1 until she was 3. But that didn't stop me from taking them of DD2 at nb, 3 mo, 6mo, 9 mo, 1 yr, 2 yrs, etc... In my experience, the second and subsequent children give mom a hard time for not having as many pictures and momentos of them as she does of #1. (realistically, there will be less photos/momentos/etc of second (etc) child(ren) because they are sharing the stage with another sibling and lots of photos are shared and not individual.) So, having a birth announcement would prob make #2 feel better about that!