Crayon Rubbing Portrait

Here's a project I've played around with this year for my preschool classroom.  Each year I draw the kid's portraits and give them to the families at the end of the year.  This year, I wanted to do something a little different and this is kind of what I came up with.  I'm still fine tuning this recipe but I really like where it's going.  Takes a little time but the results are cool and it can replicated a hundred times afterwards in multiple ways.  Let me know if you have any ideas to improve on this, always up for more fun!