We (16-24 mos.) glued big pom-poms and little pom-poms to paper. We asked the children to find the big ones (then the little ones).
I cut out all sorts of shapes (circles, squares, triangles, ovals, rectangles, etc.) I cut them in large sizes and then small sizes. let the kids paste the small ones onto the big ones that matched each shape. When they finished all the matching shapes we glued all the matches onto a large paper and made a class poster!
To show the difference between little and big, I had the children place their hand in paint and then make a handprint on a piece of construction paper. Next I had one of our teachers make their handprint right next to it. This worked well with a toddler class ages 2 – 3 yrs old.