The sleep sack can include a back panel, a front panel, and a flap. The sleep sack is used by placing the front panel over the back panel. The front panel extends from the shoulder to under the arm of the infant or toddler. The sleep sack is used by placing the flap over the front panel once placed. The flap extends from the shoulder to under the arm of the infant or toddler. The flap can be releasably attached to an outer surface of the sleep sack to adjust the compression of the torso of the infant or toddler.