Hi Jill,
I have had very good results in primary grades with crayon resist using
oil pastels rather than crayons for leaf rubbings and then having the kids
apply a purple watercolor wash. Maybe limit the colors of pastels they can
use. Orange,yellow,red and green leaves looked beautiful with the purple
wash over them.I had the kids practice doing the rubbings on newsprint
first to get the hang of it. -judy