Out of the mouths of babes
When I was pregnant with Noella, I took Mariel shopping with me in pursuit of a reasonably professional looking maternity suit (a difficult task).  I also discovered on that trip to the mall that size small was really not going to work anymore.  After some unsuccessful try ons, Mariel, age 2, ran out of the dressing room yelling "Mommy needs bigger pants!"  Fabulous.
Today, Noella carried on the tradition, although (thankfully) in a private setting.  After I got her dressed we went into my room so that I could get dressed.  As I stood there in my underwear holding up clothes she looked at me and my belly sadly, shook her head, and said "Mommy, that no fit."  Thanks kid.  And it did fit.