This is easy enough that Kavi can do almost the whole thing, start to finish. She could do all if our microwave was a little lower and easier to access. Buy candy melts, microwave them in thirty second bursts and stir until melted (about 2 min?). Spoon into heart mold. Tap it a few times on the table to get out air bubbles and smooth it out. Stick it into freezer for five minutes. Take out and pop out onto a cutting board. Trim with a sharp knife if you're feeling fussy -- that's what Kevin's doing here, but really, that step is optional. And that's it -- frozen hearts!
If you haven't done molded chocolate before, my two tips are a) use the candy melts, much easier than actual chocolate, even if they don't taste quite as good as high quality chocolate, and b) choose a simple shape -- we tried little mice with tails for my Hitchhiker's Guide party, and the tails were almost impossible to pop out without breaking. Hearts, though -- no problem!
"So cut through the heart, cold and clear.
Strike for love and strike for fear.
See the beauty, sharp and sheer
Split the ice apart
And break the frozen heart."