When the girls were first born, I thought Grace was much cuter than Sydney, but she has certainly grown on me. She is just the cutest thing darn thing.
I read somewhere that scenes with only the babies are shot independent of the other actors. What they do is take time out and film lots of things trying to get them to react (probably with her real mother).
Yes, her eyes bring a lot to her "acting." I guess maybe the credit should be going to the editor.