DH and I are often focused on DD6 and her HG stuff so when we think about DD21months we think of her in terms of her big sister. (I know, not thing you're suppose to do but...) One big difference between them is their verbal skills. DD6 was an early speaker but DD21mths wasn't nearly as early.
So, last week DH comes downstairs to have lunch with us and he comes around the corner into the kitchen and says hi to DD21mths who is sitting in her highchair, and asks what she is doing. Her response was "(name) eating snack, DD6 suppose to be eating too" We were rolling because she was right! DD6 was being goofy rolling on the floor and not eating like she was suppose to be.