Elementary school class. Geometric drawing

Geometric drawings that I do several times a year. It's a basic motif for drawing, but everyone did their best while using various types of pencils and using a brush and a kneaded eraser. How can I get along with a pencil and create a three-dimensional space in the paper? As I draw over and over again, the drawing power will be applied so that each child will permeate into the head and body.