The girls are just old enough recognize that there are definite developmental differences between them and the toddlers. If we don't notice it immediately, and comment on it, they will. Each sentence starts with "when I was little." Even though they are twins, we never hear "when we were little."
It usually goes something like this. We'll be talking about some activity, say swimming lessons. One of the girls will say, "When I was little, like three, I didn't know how to swim. Now I'm four and I can swim on my front and my back."
Sometimes the girls comment on another child's behavior. "When I was two, I used to yell in the store. Now I'm a big girl and I know better, so I don't scream in the store."
My favorite is when they repeat something we always say, "When I was little, I didn't like broccoli, but now I'm a big girl so I eat all my vegetables because they make me healthy."
Sometimes their observations are quite to the point. Other times they ramble a bit. It's funny to hear them talk about what "big girls" do that little girls do not. Every topic is fair game from eating specific food to using the toilet to brushing their teeth to hitting a baseball.
Soon they will be five, so I'm sure the observations will change. One thing won't though, and that's how funny we think it is.