Lately M has been catching on to the concept of "big" and "little." (This is generally a fun thing; of course, there are those exceptions like the day when she decided to randomly point to her stomach, saying "little tummy" and then my own, with the solemn declaration "big tummy." :-)
Yesterday we tried a new activity using the big and little concept. I took 3 nesting blocks and labeled them "little," "bigger," and "biggest." Then I walked around the house and gathered up things that were similar but came in three different sizes (spice bottles, hairbows, stuffed animals, etc).
For each set of three, I asked M "Which (bunny) is little? Put the little bunny in the little box." "Which (bunny) is bigger?" "Which bunny is biggest?", etc. Little and Biggest were no problem at all, but Bigger was confusing. It was generally a good activity; so I might do it again sometime, but if I do I will either just use two boxes or I will label the middle one "medium" and spend some time working on that concept.