From birth until baby shows signs of trying to roll over. swaddle up is specifically designed to let your baby sleep in a natural arms up position. this allows them to bring their hands to their mouth and face for true self-soothing during sleep time- resulting in more sleep for everyone. we recommend that you always swaddle up according to your babies weight and not their age. the swaddle up system should feel like a hug on your baby, keeping them snug and safe- removing any risk of excess fabric, this snug fit calms startle reflex. our sizes work as per the following; newborn: 2.2-3.8kg / 5-8.5lbs, small 3.2-6kg / 7-13lbs, medium 6-8.5kg / 13-18.5lbs, medium 6-8.5kg / 13-18.5lbs. Set Contains: ------------- 1x swaddle