Check out this crayon rubbing I made. Awesome texture, right?
I did the rubbing using homemade texture plates. They couldn't be easier to make - just hot glue on scraps of chipboard, in whatever patterns (or scribbles) you want.
I put a piece of copy paper onto my completed texture plates and used one color of crayon per texture.
So pretty, and the possibilities are endless.
If you have very young children, make the texture plates for them and have them do just the rubbing portion. But kids as young as 6 can safely make their own texture plates (with supervision, of course), particularly if you use a low temp glue gun and/or finger guards (affiliate links). Just make sure you have a lot of spare glue sticks, because once you start making texture plates, it's hard to stop!