Let's look at what we've got here. Yes, we have new life! It's beautiful and you're beautiful. But what we also have is a ball or a mound.
Get creative! Why not paint it completely white and add some black orbs for eyes. Paint in a grinning mouth and call it a skull. Too morbid, when there's a little one inside?
We can get much more horrific than that! This is Halloween after all! If you (or, more to the point, whoever is painting this) has the skill, how about painting a hand reaching out? Or a picture of a baby vampire, monster, zombie or ghoul?
Surely there's a lot of inspiration in the whole Rosemary's Baby sub-genre of horror! And who knows, looking on, what you're carrying in there? Especially if you get Dad to dress up as the adult version of the scary creature that you created!
Consider this as your blank canvas. You are restrained only by your imagination and materials. I'm not even going to include skill here, as it's the trying that counts.
Nor does it even have to be a great work of art. Simplicity and a few accessories often works just as well, if not better! Just check out what this individual did below.