some say that this product run small , so I order the large . Umm ... yeah , I do not agree that it run small . we guy be swim in it when he first start use the large at 8 month . he still be swim in it at 11 month . but , even though it be large on he , he have plenty of room , get around in he crib easily , stand up in the crib and roll all around . I be just thankful that it keep he warm at night and I do not have to worry about blanket . it have wash well and hold up well so far . I have a friend who double up she jammy at night to keep she daughter warm . it be a challenge just get one pair of jammy on we boy , I would not like try to double those up . this be much easier and it keep he warm .