Missy Gold's acting
I was observing that Missy Gold's acting in the early episodes seems so much better than in the later episodes for some reason. She also seemed to have more lines in the beginning. Her appearances/lines got smaller as she got older. Also, her relationship with Benson changed a great deal. They were a lot closer and sweeter towards each other when she was a little girl. It's like she became a teenager and her whole personality changed.
Of course, I don't have kids myself so maybe those of you who are parents won't think this is so unusual!