Since having a baby, I have a feeling my sense of time is now going to be measured by diaper sizes instead of days or months or minutes or hours. My little man came home in newborn diapers that he didn't quite fill out. All of a sudden he was growing like a weed and we moved on to size one's. Now, at 6 weeks we are moving on to size two. I can see you asking yourself"whats the big deal? Diapers are diapers.". Not when its your little man growing up so fast before your eyes and changing every day! If I had to give advice to a new mom and dad (since I have so much experience- all 6 weeks of it!!) I would tell them to enjoy size one and size two, because I'm sure size three will be here before you know it.