In order for young children to be successful in comparing sizes, they need to know and understand the associated vocabulary.  They should be familiar with words like “smallest” and “biggest”,  as well as “bigger” and “smaller”. You can introduce words like “small, medium, and large” so that children can put the items in order.

Think of things you already have in your home or classroom that come in sizes.  You might have little spoons, teaspoons and tablespoons.  These three items can be used just like those depicted above.  You can make your own cards with 3 boxes labeled small, medium and large so that children can sort the spoons accordingly.  What else do you have that comes in 3 sizes?