Sydney has a set of colored plastic cups that she's loved since well before she could walk. Initially it was just fun to bang them together. Later she would try to stack them or put one inside another. Now we're at the point where putting all of them together so that each is inside the next biggest is the goal. She is however not making much progress on that goal.
Several times in the last few weeks she's set all of the cups out and started attempting to put them inside each other. Inevitably she attempts to put a big cup inside a small one... often the largest inside the smallest. We explain that she has them backwards and she'll eventually reverse them and then grab a third. Inevitably it's too big to fit in the inside one and too small to go around the outside one. There's about 6 or 7 cups in all and when we get to cup 4 or 5 it turns into a systematic checking to see if the current cup in her hand will fit in each of the ones she has stacked up. Imaging putting them together and taking them appart over and over again, each time attempting to incorporate the next cup.
Often after a few minutes of this she starts getting frustrated.
The amazing thing to me is that she is closer to devising a systematic approach to trying every cup inside every other cup in order to put them all together than she is at recognizing that the largest cup has no chance of going in the smallest one. The concept of large and small is still a total mystery to her.
I guess the good thing is that it entertains her for quite awhile until she gets frustrated.