Thought the same thing ...
My DD was born a week after Caylee. She was often rewarded with a sticker for doing a wee on the toilet (and later, a "big, big" sticker for making a "splash" )
I'm sure if George and Cindy were spending so much time raising Caylee, then any of Caylee's stickers would be quite familar to them.
I had EXACTLY the same thought. Caylee was of an age when she should have been potty training and we know she was still in diapers.
Many parents/teachers use stickers as incentive to use the potty.
Here's yet another possibility/thought. Could Caylee's death have resulted from Casey smacking or pushing her because she went in her pants rather than on the potty?