Abstract: A baby backpack sack adapted for use with a baby backpack carrier is disclosed formed by first and second side panels and an end panel which form a partially closed container. The panels are joined together by longitudinal seams arranged generally in the shape of an inverted Y. The arrangement of the longitudinal seams permits greater expansion of a lower end of the container to accommodate a wider range of baby backpack carriers, to provide additional room for carrying other items in the baby backpack sack with the baby and especially to accommodate a collapsible stand of the baby backpack carrier. The baby backpack sack preferably includes a plurality of pockets on an outside surface of the container for carrying items such as bottles and diapers. Still further, the container includes an access slot on an outside surface of the container for facilitating access to the interior of the container when a baby is placed therein.