These do tend to run a size big depending on your babe! My daughter (older girl in photo) is wearing a size 5/6 which is her normal size with room to grow. Boy model is wearing a 6/7 and has a tons of room to grow (his normal size) and baby is wearing 12/18m but is super petite and has a ton of room to grow.
Material on PJs were sold to me as Bamboo but please note that I can not authenticate material at the time (these are super comfy, soft and very well made)