This is more like Chris and the girl vs Martha. This was a fun project we did together. It's easy simple but requires an iron so adult supervision is needed.
Martha has the instructions on her site for crayon hearts but I'll take you through the process.
First, we made the crayon shavings with a pencil sharpener. A bit of a messy job.
Then I melted the crayons between 2 sheets of wax paper. Remember to put a towel underneath the wax paper or you will have crayon melted to your ironing board (ask me how I know this) and brown paper between the iron and the top sheet. If I was to do it again, I'd spread out the crayon more- a little goes a long way.
Then we made up heart shapes with regular paper for templates and used those to cut out the hearts from the wax paper. Next I used a needle and embroidery floss to string the hearts. To show them in the window, I used a short piece of wire hiding strip- it has an adhesive strip to hold it in place.
And viola! An easy Valentine's Day decoration!