So my son is 4 months and already over 20 pounds I'm sure. (Dr appt not till 20th) but last month we went to the er he was 19.8 . Ha. Already can for 18 month clothing without being too loose. 9 month is too right and can't for over his diaper. 12 is perfect fit but snug .
he's a chunky baby and all he eats is milk :)