Cozy Sleep Sacks will have your child sleeping in comfort! double layered organic cotton design is warm and breathable. sleepsack fits perfectly over our footie pajamas for cool evenings or can be paired with a onesie for warmer nights. In addition our sleep sack encourages baby to sleep on their back until they can comfortably roll over from their back or tummy and eliminates loose crib blankets for the prevention of SIDS. • Small - 3-6 mo 10-18 lb • Medium - 6-18 mo 16-24 lb.