Here’s what we did.
I gave each child a sheet of sandpaper (turns out fine grit works best but we had coarse) and had them each draw a picture nice and heavy with good quality crayons.
We cut out the designs and positioned them over light colored, cotton shirts. I put paper inside the shirt to keep the crayon from bleeding through and ironed on cotton setting for a couple of minutes, giving bursts of steam to further heat it up.
We let it cool a minute and then gently peeled off the sandpaper. Then I put a piece of waxed paper down and ironed over that to further set the design. Again, we waited a minute for it to cool and then we lifted it off.
The finished designs are not as bright or clear as the originals on the sandpaper but they are really neat. It does help to really color the design fully and make it nice and thick.
Be sure to climb trees while waiting your turn to do your shirt.
Last step: frolic.