I made some fondant/gum paste ladybugs for cupcake toppers a couple days ago. Today, they're still really soft. I'm almost 100% positive that I put gum paste in it so that they should have hardened. (they're flat) I remember reading somewhere that they're something I can brush on them to make them harden? Am I wrong?

I don't think there's anything that will actually harden the fondant. However, if you need them to stand up, you can "paint" the back with melted chocolate and when it cools/hardens, then you can stand them up.

HTH