I know every baby's different, but my SIL keeps making comments b/c she can't believe DD's already wearing a Size 4 diaper at 9 1/2 months. Her son is 16 months and in a size 4, so she keeps making weird remarks about it. Size 3s started giving DD diaper wedgies so we moved her to size 4 a couple of weeks ago.
DD is in the 50th percentile for weight and height, so it's not like she's a huge baby or anything. What size diaper does your 9-month old wear?