I can't take credit for this broken crayon project, found it on Pinterest, but I tried it out and it worked GREAT! Nice alternative to candy Valentine's. Most classrooms have an abundance of broken crayons. I bet they would trade you a new box for a bunch of broken ones.
TIP: To get the crayons peeled, get a small box knife and hold one end with one hand and drag the knife blade from those fingers down the middle to slit it open. Saves a ton of time. We taught our 7 and 10 year olds how to use the box knife to do this. I was only stuck doing the really short broken pieces.
Then, you can use those silicon cupcake holders. I decided to buy a dozen separate ones instead of one tray with 8 or 12. It was less at Michaels and I like the ridges around the cupcakes. The silicon are better than using Whoopie pie pans or similar because you can bend them away to pop the crayon hearts out. This is great for any season.
Small chunks, but not too small - about an inch work best.
Fill a cupcake holder half way. Bake for 15 minutes at 325 degrees. Take out and let cool completely before popping them out. You may need to smooth the top of the heart, depending on how lumpy your crayons are. Some pigments seems to melt differently, as do washable vs. regular crayons. Great use for those dopey restaurant crayons. No need to wash the holders between batches, just wait unti you are done.