Small - 10 to 18 pounds who are generally 0-6 months old and 23-26"" long, medium - 16 to 24 pounds who are generally 6-12 months old and 26-30"" long, large - 22 and 28 pounds who are generally 12-18 months old and 30-35"" long, x-large - 26 and 38 pounds who are generally 18-24 months old and 35-40"" long, ultra-soft and breathable cotton - Comfy Cubs sleep bag, sack for newborns and growing toddlers are woven with 100% natural cotton that's double knit for strength and cool breathability, so they help wick away sweat and moisture while they sleep. Covered zipped for convenient and safety - our sleep bag, sack for kids feature an easy-zip front that lets you slide them in or out quickly with a zipper that's hidden within the seams and protected by a snap-front closure that prevents pokes or scratches. Optimal mobility and movement - the wider base of our Comfy Cubs sleep bag, sack allows children to roll, move, kick, and flex their legs which is important for growth, hip health, and general body awareness, which makes them great for babies. Cute and comfy baby sleepwear - these kid's sleep bag and sack are designed for comfort, style, and sleep support thanks to a quick zippered front, sleeveless top, and super roomy footed area that lets kids move and relax from head to toe.