There are actually a lot of elements to teaching and learning shapes because there are a variety of 2-dimensional shapes and 3-dimensional shapes that are distinguished by lines, angles, bases, sides, etc. And believe it or not, 2 and 3-dimesional shapes are introduced in Kindergarten, as well as tangrams (combining shapes together to form images), and sorting shapes by two attributes. So children definitely need to learn their basic shapes, and learn them well, early on because there is more to come!
If I were to teach my son shapes I would start with one a day, or even one a week, and investigate it, study it, and have fun with it, in as many ways possible.
Below is a link of a pair of glasses I made that I want you to print onto cardstock, cut out, and then draw the shape you and your child are “studying” onto the middle of the lens where the eyes would look out. Talk about the shape while you are drawing it. For example, if you were drawing a square you might say something like “I am going to make our holes in the shape of a square. So to make a square I need to start at the top, draw a straight line down, across, up, and back. Let’s count how many sides a square has! Do you want to trace over it with a marker the same way I drew it? What else do you notice about it? What does it remind you of? “
Draw it on the other lens and then cut them out carefully by poking a hole in the center and cutting outward, or bending the glasses and starting the snip that way.

Now go on a search all around your house with your “shape goggles” to find as many of that shape as you can.
Shape Glasses