I purchased size 7-12 month for my 6 month old son who weighs 19 lbs and usually wears size 9-12 month.  The top fit pretty well but the pants were too small.  There was barely enough room in the seat of the pants to fit his diaper and the pant length was okay, but there was no way the suspenders were going to work as is.  They were so short moving the buttons would barely even work.  I was considering keeping this outfit and altering it myself because I didn't have much time before the event my son was to wear this to, but the pants were also missing a snap.  There were just too many issues so I ended up returning it.