Children are typically visual learners. This tutorial gives you the framework to create a class focussed on proper stances and hand placement. Using masking tape or painters tape, you can map out a pattern on the mat/floor for the students to follow.
In the second portion, they used a piece of tape placed on the wall to give the student a visual target; practicing using this method reinforces muscle memory.
Tip: Write the proper distances for the stances and arm placement out ahead of time, then when the class is over, you can email it to the parents, the students can practice it later as homework.