What happens at a blessingway, anyway? I don't really know much about them...

Okay, taking a couple of ideas from here, how about this at the top of the invitation?

The babe dubbed Cookie is on the way, so please join us in celebrating their imminent arrival with a day full of fun, laughter, happiness and rainbows!
I'd like to add in a couple more things, like an instruction to bring an apron and/or wear casual clothes (one of the game things I might want to do might get a little messy) and the like...