This is an oldie, but goodie. Start by grating up some crayons. The cheap-o crayons were much easier to grate because they are softer, and they melt nicely, too.
Sprinkle grated crayon onto wax paper.
For a second, fun craft (and since you already have the crayon grated), sprinkle some on white construction paper or water color paper.
Put another piece of wax paper on top, and iron on low to melt crayon. Let cool. You may want to put a towel on top and bottom to protect your ironing board and iron, but you will probably need to turn the heat up a little. Cut out hearts.
We used a hole punch and hung ours with ribbon in front of the window.
Now, back to the white paper. When you iron it, place a piece of wax paper on top to iron (and a towel if desired) and then remove it after the crayon is melted. When it is cool, use water colors to paint. The color will only show on the white space.
Cut into hearts.
I think these Valentines turned out lovely.