Teaching kids about primary and secondary colors is very technical. However, through hands on experience, they will be able to understand these technical terms.
First thing to do is to show them the basic colors or the primary colors such as red, blue and yellow. Let the children identify the colors and tell them that all those colors are primary colors.
After that, start mixing two primary colors like red and blue, red and yellow and blue and yellow. Allow the children to identify the colors that they see after mixing colors. Then, let them share how those colors were formed. Emphasize to them that secondary colors are created when two primary colors are mixed.
Finally, let the children make a basic color wheel by using the paint that they used in mixing colors.
Children learn through repetition. And so, you may recap again what primary colors and secondary colors are. You can also have extension activity wherein you will play a game and ask the children to identify the primary and secondary colors in the environment.