I chose M because I could let my hands out. I was able to use it with peace of mind during the time when my baby was sucking on their fingers and rolling over. I used it from about 2 to 6 months old. Even when my baby was a little bigger, the most constricted part was relatively stable, and they were sleeping soundly. It might be a little inconvenient when they start to stand up, but it's very stretchy and doesn't constrict, so it seemed very comfortable to wear. It's cute, like a sea angel. ◇ Night Crying Measures, Sleep Well, Wearable Swaddle ◇ 【Product Description】 ■ Sleep soundly without stress The baby's arms and legs are free, allowing for a natural posture and peace of mind. ■ Gentle, soft touch 95% cotton for comfort all season long Good breathability, stretch, and absorbency ■ Easy diaper changes Double zippers make it convenient to change diapers while wearing 【Product Details】 Product Name: Swaddle, Swaddler, Sleeper, Baby Shower Gift, Cute, Winter, Spring, Hospital Discharge, Newborn, Baby, Sleep Aid, Baby Clothes, Moro Reflex, Stylish, Nekurumi ●Sizes S size: Total length approx. 60cm, Estimated: 3-6kg, 0-3 months (sleeveless) M size: Total length approx. 67cm, Estimated: 6-8.5kg, 3-6 months (2in1 sleeves) L size: Total length approx. 75cm, Estimated: 8.5-11kg, 6-12 months (2in1 sleeves) ※This is just a guide, and there may be individual differences. Please check the size before considering. ●Colors Gray Blue ●Material Cotton