Thanks everyone! I haven't been online all day so I'm just seeing these comments.
I'm thinking it will fit a 6-9 month old. It only measures about 17" around, but my first one measured only 20". The gauge was right and it was supposed to be 25" after blocking, but my yarn was not wool and I didn't block it as hard. This little one I wanted to avoid blocking because although I wouldn't say I killed the yarn, it is definitely softer. It will stretch quite a bit beyond its 17".
I like seed st too and I was hoping it wouldn't need blocking as much as the St st right against the Rev St st, and I think it worked.
I made this sweater 18 sts smaller than the smallest one in Sarah's pattern