I bought these before my baby was born in size 0-3 month and was a little disappointed after washing them that they were still really big. They didn't fit my baby until he was about 2 and a half months, but I instantly loved them. The zipper zips from bottom to top so you don't have to completely undress your baby for diaper changes and the material is very light, great for California weather where it doesn't really get too cold. I recently bought some more in the next size up and they are pretty much the exact size as the 0-3 ones I bought a few months ago, so maybe I just got some weird ones. Oh well.