Congragulation letter for new born baby?

Do you want to know what to write? I would say something like: I am so excited to meet your little bundle of joy! Congrats! (if you haven't seen the baby) If you have seen the baby: Oh, your baby is soooooooooo cute, you lucky duck! Congratulations on your new bundle of joy!





But then, what do I know. I've never sent a 'congrats on your baby' card. I'm a kid.