When teaching a class on how to draw animals, we covered mostly graphite and colored pencils, but one of my students wanted to draw with crayons. It was fun cracking open the box of Crayolas and giving the class a demonstration. I shared the illustrations I had done for the book, and we analyzed the characteristics of drawing with crayons.
Consistent Pressure Gives a Uniform Look. Keeping a consistent pressure with the crayon on the paper gives a uniform, pleasing look. If you're pressing hard, your hands will get tired quickly, so I prefer to press lightly. Interestingly, being aware of how much pressure you're applying seems to be really hard for younger children. It must be tied to motor skills in some way. It won't hurt anything to tell them this tip, but if they aren't implementing it, just let it go.