How about mixing colors with water or icing.

Like: red and blue makes purple

red and yellow makes orange, etc.

I’ve taught it to my 1st graders both ways. They especially liked the icing because they could eat it. (after they showed me how to make all the colors that I instructed them to make.)

I just bought white icing and used food coloring. Each child had a paper plate with little dabs of each primary color to begin. They love it! Good luck! Teaching is awesome!

The beginning of the lesson could include you asking them about shapes and what they know about them.

The middle will be reviewing each one and the number of sides and angles. Explain the difference between the square and rectangle because they both have the same number of sides and angles.

Then end could be for the students to find things in the room that represent each one… the clock is a circle, the table is a rectangle, etc.

Good Luck!