I have recently taken measurements of this sweater and compared to baby size charts. According to my measurements this sweater is really a 6-9 month size.

Neckline: 12”
Chest: 19” measured just under arms
Neck to bottom edge: 10.5”
Sleeve: 4” from underarm to wrist
8” from shoulder to wrist

I have noticed that a lot of knit patterns call for a 5” sleeve so I would now work 10 sleeve rows of dc instead of 8.