I own one of these sleep sack for my infant son , and I love they so much I decide to order one through Amazon . I do not know if the stock be different , but the medium that I order be way too small . my son be 16 pound and I can barely loop he arm through the arm hole . he be a pretty lean baby , so I doubt that body shape be a issue . besides , the other one that we have -lrb- and that we order through a different site -rrb- be great -- there be still room for he to grow into it , which be how it should be , consider that the weight range be intend to be from 15-24 pound . it be too bad , because we really like aden + anai in general .