pregnancy announcement ideas?

I'm waiting to announce on Fb. I told my parents, my boss and some of my close friends and told them not to tell, so naturally pretty much everyone knows, but I'm still waiting to formally announce. I'm trying to find ways to get my 6 year old excited about being a big sister and thought to make her the focal point. I was thinking a sign that says "I asked Santa for a unicorn but mom and dad said I'm getting a brother or sister instead" I'm due 12-14. any other fun ideas that she could be the one to announce? how are you guys announcing and when?