The best way to ‘teach’ toddlers is to provide stimulating activities. When I worked at the nursery, we would focus on one topic each week and provide various activities that the children would enjoy and learn from.
I would stick to the basics, circle, square and triangle.
Art & Craft
A Shape Collage – Pre-cut shapes from coloured paper, let your toddler stick them down onto a piece of card.
A Shape Mobile – Cut large shapes from thick card, punch a hole and thread with string.
Traffic Light Picture – A traffic light picture (black card, three circles painted in red, yellow and green) combines shape and colour.
Balls – Play catch or make your own ball pool.
Building Blocks – Build towers and interesting shapes.
Shape Sorter Toys – Shape sorter toys include the light and sound variety as well as the wooden block style. We have both and they are equally good.
Make your own cards, cut 12 cards, make 4 for each shape and play snap.
My First Jumbo Book of Shapes looks like a good pick, I haven’t read it but it does have a good write up and it is age appropriate, it also says that it is ‘wonderfully interactive’ and young children *love* to get involved.