Crayons can be recycled into almost any shape. I used the LEGO Minifigure Ice Cube Tray
While working with melted wax may be something for aparent to do, even little ones can help make these by stripping the crayons, sorting them, and breaking them up.
living peacefully with children 
How adorable!
I have *always* thought making molded crayons would be a fun project to do! Do you use new crayons? If not, where do you find enough old crayons for such a project?
And have you ever tried swirling the colors?
If you ask around, everyone seems to have a bag of broken crayons they would like to get rid of.