My 4-month-old wears a size 2, but I have to say, it's not a great fit. She's 16 lbs with HUGE thighs (bigger than my 3-year-old's), and the width of the crotch is just ridiculous on her. I reach for it last because the bulk is just too much. And I usually am not one who cares about bulk. I'm going to hang onto it, though, because I'm guessing it will be awesome when she's a toddler.
Rebecca, married to J (2007), DD1 Anna (11/09) and DD2 Ada born at home 7/12 DS Henry born at home 3/14